(Slip Opinion)              OCTOBER TERM, 2011                                       1

                                       Syllabus

         NOTE: Where it is feasible, a syllabus (headnote) will be released, as is
       being done in connection with this case, at the time the opinion is issued.
       The syllabus constitutes no part of the opinion of the Court but has been
       prepared by the Reporter of Decisions for the convenience of the reader.
       See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337.


SUPREME COURT OF THE UNITED STATES

                                       Syllabus

                 PPL MONTANA, LLC v. MONTANA

       CERTIORARI TO THE SUPREME COURT OF MONTANA

  No. 10–218.     Argued December 7, 2011—Decided February 22, 2012
Petitioner PPL Montana, LLC (PPL), owns and operates hydroelectric
  facilities in Montana. Ten of its facilities are located on riverbeds
  underlying segments of the Missouri, Madison, and Clark Fork Riv-
  ers. Five hydroelectric dams on the Upper Missouri River are along
  the Great Falls reach, including on the three tallest waterfalls; and
  PPL’s two other dams on that river are in canyons on the Stubbs Fer-
  ry stretch. These, together with two dams located in steep canyons
  on the Madison River, are called the Missouri-Madison project. The
  Thompson Falls project is a facility on the Clark Fork River. Both
  projects are licensed by the Federal Energy Regulatory Commission.
  PPL’s facilities have existed for many decades, some for over a centu-
  ry. Until recently, Montana, though aware of the projects’ existence,
  sought no rent for use of the riverbeds. Instead, the understanding of
  PPL and the United States is that PPL has paid rents to the United
  States. In 2003, parents of Montana schoolchildren filed a federal
  suit, claiming that PPL’s facilities were on riverbeds that were state
  owned and part of Montana’s school trust lands. The State joined the
  suit and, for the first time, sought rents from PPL for its use of the
  riverbeds. That case was dismissed, and PPL and other power com-
  panies filed a state-court suit, claiming that Montana was barred
  from seeking compensation for PPL’s riverbed use. Montana coun-
  terclaimed, contending that under the equal-footing doctrine it owns
  the riverbeds and can charge rent for their use. The trial court
  granted Montana summary judgment as to navigability for purposes
  of determining riverbed title and ordered PPL to pay Montana $41
  million in rent for riverbed use between 2000 and 2007. The Mon-
  tana Supreme Court affirmed. Adopting a liberal construction of the
  navigability test, it discounted this Court’s approach of considering
  the navigability of particular river segments for purposes of deter-
2                  PPL MONTANA, LLC v. MONTANA

                                  Syllabus

    mining whether a State acquired title to the riverbeds underlying
    those segments at the time of statehood. Instead, the Montana court
    declared the river stretches in question to be short interruptions of
    navigability that were insufficient as a matter of law to find nonnavi-
    gability, since traffic had circumvented those stretches by portage.
    Based on evidence of present-day, recreational use of the Madison
    River, the court found that river navigable as a matter of law at the
    time of statehood.
Held: The Montana Supreme Court’s ruling that Montana owns and
 may charge for use of the riverbeds at issue was based on an infirm
 legal understanding of this Court’s rules of navigability for title un-
 der the equal-footing doctrine. Pp. 10–26.
    (a) The rule that the States, in their capacity as sovereigns, hold
 “title in the soil of rivers really navigable,” Shively v. Bowlby, 152
 U. S. 1, 31, has federal constitutional significance under the equal-
 footing doctrine. Pursuant to that doctrine, upon its date of state-
 hood, a State gains title within its borders to the beds of waters then
 navigable. It may allocate and govern those lands according to state
 law subject only to the United States’ power “to control such waters
 for purposes of navigation in interstate and foreign commerce.” Unit-
 ed States v. Oregon, 295 U. S. 1, 14. The United States retains title
 vested in it before statehood to land beneath waters not then naviga-
 ble. To be navigable for purposes of title under the equal-footing doc-
 trine, rivers must be “navigable in fact,” meaning “they are used, or
 are susceptible of being used, . . . as highways for commerce, over
 which trade and travel are or may be conducted in the customary
 modes of trade and travel on water.” The Daniel Ball, 10 Wall. 557,
 563. This formulation has been used to determine questions of wa-
 terbed title under the equal-footing doctrine. See United States v.
 Utah, 283 U. S. 64, 76. Pp. 10–14.
    (b) The Montana Supreme Court erred in its treatment of the ques-
 tion of river segments and portage. To determine riverbed title under
 the equal-footing doctrine, this Court considers the river on a seg-
 ment-by-segment basis to assess whether the segment of the river,
 under which the riverbed in dispute lies, is navigable or not. See,
 e.g., Utah, supra, at 77. The State Supreme Court erred in discount-
 ing this well-settled approach. A key justification for sovereign own-
 ership of navigable riverbeds is that a contrary rule would allow pri-
 vate riverbed owners to erect improvements on the riverbeds that
 could interfere with the public’s right to use the waters as a highway
 for commerce. Because commerce could not have occurred on seg-
 ments nonnavigable at the time of statehood, there is no reason to
 deem those segments owned by the State under the equal-footing
 doctrine. Practical considerations also support segmentation. Physi-
                   Cite as: 565 U. S. ____ (2012)                      3

                              Syllabus

cal conditions affecting navigability vary over the length of a river
and provide a means to determine appropriate start points and end
points for disputed segments. A segment approach is also consistent
with the manner in which private parties seek to establish riverbed
title. Montana cannot suggest that segmentation is inadministrable
when the state courts managed to apportion the underlying riverbeds
for purposes of determining their value and PPL’s corresponding
rents. The State Supreme Court’s view that the segment-by-segment
approach does not apply to short interruptions of navigability is not
supported by this Court’s Utah decision. Even if the law might find
some nonnavigable segments so minimal that they merit treatment
as part of a longer, navigable reach, it is doubtful that the segments
in this case would meet that standard. Applying its “short interrup-
tions” approach, the State Supreme Court found the Great Falls
reach navigable because it could be managed by way of land route
portage, as done by Lewis and Clark. But a portage of even one day
would demonstrate the need to bypass a nonnavigable river segment.
Thus, the State Supreme Court was wrong to conclude, with respect
to the Great Falls reach and other disputed stretches, that portages
were insufficient to defeat a navigability finding. In most cases, they
are, because they require transportation over land rather than over
the water. This is the case at least as to the Great Falls reach. In
reaching a contrary conclusion, the State Supreme Court misapplied
The Montello, 20 Wall. 430. There, portage was considered in deter-
mining whether a river was part of a channel of interstate commerce
for federal regulatory purposes. The Montello does not control the
outcome where the quite different concerns of the riverbed title con-
text apply. Portages may defeat navigability for title purposes, and
do so with respect to the Great Falls reach. Montana does not dis-
pute that overland portage was necessary to traverse that reach, and
the trial court noted the waterfalls had never been navigated. The
Great Falls reach, at least from the head of the first waterfall to the
foot of the last, is not navigable for purposes of riverbed title under
the equal-footing doctrine. There is also a significant likelihood that
some of the other river stretches in dispute fail this federal navigabil-
ity test. The ultimate decision as to these other disputed river
stretches is to be determined, in the first instance, by the Montana
courts on remand, which should assess the relevant evidence in light
of the principles discussed here. Pp. 14–21.
   (c) The Montana Supreme Court further erred as a matter of law in
relying on evidence of present-day, primarily recreational use of the
Madison River. Navigability must be assessed as of the time of
statehood, and it concerns a river’s usefulness for “ ‘trade and trav-
el.’ ” Utah, 283 U. S., at 75–76. River segments are navigable if they
4                   PPL MONTANA, LLC v. MONTANA

                                   Syllabus

    “ ‘[were]’ ” used and if they “ ‘[were] susceptible of being used’ ” as
    highways of commerce at the time of statehood. Id., at 76. Evidence
    of recreational use and poststatehood evidence may bear on suscepti-
    bility of commercial use at the time of statehood. See id., at 82–83.
    In order for present-day use to have a bearing on navigability at
    statehood, (1) the watercraft must be meaningfully similar to those in
    customary use for trade and travel at the time of statehood, and
    (2) the river’s poststatehood condition may not be materially different
    from its physical condition at statehood. The State Supreme Court
    offered no indication that it made these necessary findings. Pp. 21–
    24.
        (d) Because this analysis is sufficient to require reversal here, the
    Court declines to decide whether the State Supreme Court also erred
    as to the burden of proof regarding navigability. P. 24.
        (e) Montana’s suggestion that denying the State title to the disput-
    ed riverbeds will undermine the public trust doctrine—which con-
    cerns public access to the waters above those beds for navigation,
    fishing, and other recreational uses—underscores its misapprehen-
    sion of the equal-footing and public trust doctrines. Unlike the equal-
    footing doctrine, which is the constitutional foundation for the navi-
    gability rule of riverbed title, the scope of the public trust over waters
    within the State’s borders is a matter of state law, subject to federal
    regulatory power. Pp. 24–25.
        (f) This Court does not reach the question whether, by virtue of
    Montana’s sovereignty, neither laches nor estoppel could apply to bar
    the State’s claim. Still, the reliance by PPL and its predecessors in ti-
    tle on the State’s long failure to assert title to the riverbeds is some
    evidence supporting the conclusion that the river segments over
    those beds were nonnavigable for purposes of the equal-footing doc-
    trine. Pp. 25–26.
2010 MT 64, 355 Mont. 402, 229 P. 3d 421, reversed and remanded.

    KENNEDY, J., delivered the opinion for a unanimous Court.
                        Cite as: 565 U. S. ____ (2012)                              1

                             Opinion of the Court

     NOTICE: This opinion is subject to formal revision before publication in the
     preliminary print of the United States Reports. Readers are requested to
     notify the Reporter of Decisions, Supreme Court of the United States, Wash­
     ington, D. C. 20543, of any typographical or other formal errors, in order
     that corrections may be made before the preliminary print goes to press.


SUPREME COURT OF THE UNITED STATES
                                   _________________

                                   No. 10–218
                                   _________________


   PPL MONTANA, LLC, PETITIONER v. MONTANA
    ON WRIT OF CERTIORARI TO THE SUPREME COURT OF

                      MONTANA

                              [February 22, 2012]


   JUSTICE KENNEDY delivered the opinion of the Court.
   This case concerns three rivers which flow through
Montana and then beyond its borders. The question is
whether discrete, identifiable segments of these rivers in
Montana were nonnavigable, as federal law defines that
concept for purposes of determining whether the State
acquired title to the riverbeds underlying those segments,
when the State entered the Union in 1889. Montana
contends that the rivers must be found navigable at the
disputed locations. From this premise, the State asserts
that in 1889 it gained title to the disputed riverbeds under
the constitutional equal-footing doctrine. Based on its
title claims, Montana sought compensation from PPL
Montana, LLC, a power company, for its use of the riv­
erbeds for hydroelectric projects. The Montana courts
granted summary judgment on title to Montana, awarding
it $41 million in rent for the riverbeds for the period from
2000 to 2007 alone. That judgment must be reversed.
                             I
  The three rivers in question are the Missouri River, the
Madison River, and the Clark Fork River. The Missouri
and the Madison are on the eastern side of the Continen­
2             PPL MONTANA, LLC v. MONTANA

                     Opinion of the Court

tal Divide. The Madison flows into the Missouri, which
then continues at length to its junction with the Missis­
sippi River. The Clark Fork River is on the western side
of the Continental Divide. Its waters join the Columbia
River system that flows into the Pacific Ocean. Each river
shall be described in somewhat more detail.
                             A
   The Missouri River originates in Montana and traverses
seven States before a point just north of St. Louis where
it joins the Mississippi. 19 Encyclopedia Americana 270
(int’l ed. 2006). If considered with the continuous path
formed by certain streams that provide the Missouri Riv­
er’s headwaters, the Missouri is over 2,500 miles long, the
longest river in the United States. Ibid. The Missouri
River’s basin (the land area drained by the river) is the
second largest in the Nation, surpassed only by the Mis­
sissippi River basin of which it is a part. Rivers of North
America 427 (A. Benke & C. Cushing eds. 2005) (hereinaf­
ter Rivers of North America). As a historical matter, the
river shifted and flooded often, and contained many sand­
bars, islands, and unstable banks. Id., at 432–433. The
river was once described as one of the most “variable
beings in creation,” as “inconstant [as] the action of the
jury,” Sioux City Register (Mar. 28, 1868); and its high
quantity of downstream sediment flow spawned its nick­
name, the “Big Muddy,” Rivers of North America 433.
   The upstream part of the Missouri River in Montana,
known as the Upper Missouri River, is better charac­
terized as rocky rather than muddy. While one usually
thinks of the Missouri River as flowing generally south, as
indeed it does beginning in North Dakota, the Upper
Missouri in Montana flows north from its principal head­
waters at Three Forks, which is located about 4,000 feet
above sea level in the Rocky Mountain area of southwest­
ern Montana. It descends through scenic mountain ter­
                  Cite as: 565 U. S. ____ (2012)            3

                      Opinion of the Court

rain including the deep gorge at the Gates of the Moun­
tains; turns eastward through the Great Falls reach,
cascading over a roughly 10-mile stretch of cataracts and
rapids over which the river drops more than 400 feet; and
courses swiftly to Fort Benton, a 19th-century fur trading
post, before progressing farther east into North Dakota
and on to the Great Plains. 19 Encyclopedia Americana,
supra, at 270; 8 New Encyclopaedia Britannica 190 (15th
ed. 2007) (hereinafter Encyclopaedia Britannica); 2 Co­
lumbia Gazetteer of the World 2452 (2d ed. 2008) (here-
inafter Columbia Gazetteer); F. Warner, Montana and the
Northwest Territory 75 (1879). In 1891, just after Mon­
tana became a State, the Upper Missouri River above Fort
Benton was “seriously obstructed by numerous rapids and
rocks,” and the 168-mile portion flowing eastward “[f]rom
Fort Benton to Carroll, Mont., [was] called the rocky riv­
er.” Annual Report of the Chief of Engineers, U. S. Army
(1891), in 2 H. R. Exec. Doc. No. 1, 52d Cong., 1st Sess., pt.
2, pp. 275–276 (1891) (hereinafter H. R. Exec. Doc.).
   The Great Falls exemplify the rocky, rapid character
of the Upper Missouri. They consist of five cascade-like
waterfalls located over a stretch of the Upper Missouri
leading downstream from the city of Great Falls in mid­
western Montana. The waterfall farthest downstream,
and the one first encountered by Meriwether Lewis and
William Clark when they led their remarkable expedition
through the American West in 1805, is the eponymous
“Great Falls,” the tallest of the five falls at 87 feet. W.
Clark, Dear Brother: Letters of William Clark to Jonathan
Clark 109, n. 5 (J. Holmberg ed. 2002) (hereinafter Dear
Brother). Lewis recorded observations of this “sublimely
grand specticle”:
    “[T]he whole body of water passes with incredible
    swiftness. . . . over a precipice of at least eighty feet
    . . . . [T]he irregular and somewhat projecting rocks
4             PPL MONTANA, LLC v. MONTANA

                     Opinion of the Court

    below receives the water . . . and brakes it into a per­
    fect white foam which assumes a thousand forms in
    a moment sometimes flying up in jets . . . [that] are
    scarcely formed before large roling bodies of the same
    beaten and foaming water is thrown over and conceals
    them. . . . [T]he [rainbow] reflection of the sun on the
    sprey or mist . . . adds not a little to the beauty of this
    majestically grand senery.” The Lewis and Clark
    Journals: An American Epic of Discovery 129 (G.
    Moulton ed. 2003) (hereinafter Lewis and Clark Jour­
    nals); The Journals of Lewis and Clark 136–138 (B.
    DeVoto ed. 1981).
  If one proceeds alongside the river upstream from Great
Falls, as Lewis did in scouting the river for the expedition,
the other four falls in order are “Crooked Falls” (19 feet
high); “Rainbow Falls” (48 feet), which Lewis called “one of
the most bea[u]tifull objects in nature”; “Colter Falls” (7
feet), and “Black Eagle Falls” (26 feet). See Lewis and
Clark Journals 131–132; Dear Brother 109, n. 5; P. Cut-
right, Lewis & Clark: Pioneering Naturalists 154–156
(2003). Despite the falls’ beauty, Lewis could see that
their steep cliffs and swift waters would impede progress
on the river, which had been the expedition’s upstream
course for so many months. The party proceeded over a
more circuitous land route by means of portage, circum­
venting the Great Falls and their surrounding reach of
river before returning to travel upon the river about a
month later. See Lewis and Clark Journals 126–152.
  The Upper Missouri River, both around and further
upstream of the Great Falls, shares the precipitous and
fast-moving character of the falls themselves. As it moves
downstream over the Great Falls reach, a 17-mile stretch
that begins somewhat above the head of Black Eagle Falls,
the river quickly descends about 520 feet in elevation, see
Montana Power Co. v. Federal Power Comm’n, 185 F. 2d
                 Cite as: 565 U. S. ____ (2012)          5

                     Opinion of the Court

491 (CADC 1950); 2010 MT 64, ¶¶29–30, 108–109, 355
Mont. 402, 416, 442, 229 P. 3d 421, 433, 449, dropping
over 400 feet within 10 miles from the first rapid to the
foot of Great Falls, Parker, Black Eagle Falls Dam, 27
Transactions of the Am. Soc. of Civil Engineers 56 (1892).
In 1879, that stretch was a “constant succession of rapids
and falls.” Warner, supra, at 75; see also 9 The Journals
of the Lewis & Clark Expedition 171 (G. Moulton ed. 1995)
(hereinafter Journals of the Lewis & Clark Expedition) (“a
continued rapid the whole way for 17 miles”). Lewis noted
the water was so swift over the area that buffalo were
swept over the cataracts in “considerable quantities” and
were “instantly crushed.” Lewis and Clark Journals 136–
137. Well above the Great Falls reach, the Stubbs Ferry
stretch of the river from Helena to Cascade also had steep
gradient and was “much obstructed by rocks and danger­
ous rapids.” Report of the Secretary of War, 2 H. R. Doc.
No. 2, 54th Cong., 1st Sess., pt. 1, p. 301 (1895).
                             B
  The second river to be considered is the Madison, one
of the Missouri River’s headwater tributaries. Named by
Lewis and Clark for then-Secretary of State James Madi­
son, the Madison River courses west out of the Northern
Rocky Mountains of Wyoming and Montana in what is
now Yellowstone National Park, then runs north and
merges with the Jefferson and Gallatin Rivers at Three
Forks, Montana, to form the Upper Missouri. Lewis and
Clark Journals 158; Rivers of North America 459; 7 En-
cyclopaedia Britannica 658; 2 Columbia Gazetteer 2242.
Along its path, the Madison River flows through two lakes
artificially created by dams built in canyons: Hebgen Lake
and Ennis Lake. Federal Writers’ Project of the Work
Projects Administration, Montana: A State Guide Book
356 (J. Stahlberg ed. 1949); R. Aarstad, E. Arguimbau, E.
Baumler, C. Porsild, & B. Shovers, Montana Place Names
6              PPL MONTANA, LLC v. MONTANA

                      Opinion of the Court

from Alzada to Zortman: A Montana Historical Society
Guide 166 (2009).
                              C
  The third river at issue in this case is the Clark Fork.
That river, which consists in large part of “long, narrow
streams confined by mountainous terrain,” rises at an ele-
vation of about 5,000 feet in the Silver Bow Mountains
of southwestern Montana. 3 Encyclopaedia Britannica
352; Dept. of Interior, U. S. Geological Survey, J. Stevens
& F. Henshaw, Surface Water Supply of the United
States, 1907–8, Water-Supply Paper 252, pp. 81–82
(1910). The river flows northward for about 40 miles;
turns northwest for a stretch; then turns abruptly north­
east for a short stint, by which time it has descended
nearly 2,500 feet in altitude. It then resumes a north­
westward course until it empties into Lake Pend Oreille in
northern Idaho, out of which flows a tributary to the Co­
lumbia River of the Pacific Northwest. Ibid.; 1 Columbia
Gazetteer 816. The Clark Fork is “one of the wildest and
most picturesque streams in the West,” marked by “many
waterfalls and boxed gorges.” Federal Writers’ Projects of
the Works Progress Administration, Idaho: A Guide in
Word and Picture 230 (2d ed. 1950).
  Lewis and Clark knew of the Clark Fork River but did
not try to navigate it, in part because the absence of salm­
on in one of its tributaries made Lewis believe “ ‘there
must be a considerable fall in [the river] below.’ ” H. Fritz,
The Lewis and Clark Expedition 38–39 (2004). This was
correct, for shortly before the Clark Fork exits to Idaho
from the northwest corner of Montana, “the waters of the
river dash madly along their rocky bed,” dropping over 30
feet in a half-mile as they rush over falls and rapids in­
cluding a “foaming waterfall” now known as Thompson
Falls. O. Rand, A Vacation Excursion: From Massachu­
setts Bay to Puget Sound 176–177 (1884); C. Kirk, A
                 Cite as: 565 U. S. ____ (2012)            7

                     Opinion of the Court

History of the Montana Power Company 231 (2008).
                               II
   Petitioner PPL Montana, LLC (PPL), owns and operates
hydroelectric facilities that serve Montana residents and
businesses. Ten of its facilities are built upon riverbeds
underlying segments of the Upper Missouri, Madison, and
Clark Fork Rivers. It is these beds to which title is
disputed.
   On the Upper Missouri River, PPL has seven hydroelec­
tric dams. Five of them are along the Great Falls reach,
including on the three tallest falls; and the other two are
in canyons upstream on the Stubbs Ferry stretch. See K.
Robison, Cascade County and Great Falls 56 (2011); Aar­
stad et al., supra, at 125, 119, 145–146. On the Madison
River, two hydroelectric dams are located in steep can­
yons. On the Clark Fork River, a hydroelectric facility is
constructed on the Thompson Falls.
   The dams on the Upper Missouri and Madison are
called the Missouri-Madison project. The Thompson Falls
facility is called the Thompson Falls project. Both projects
are licensed by the Federal Energy Regulatory Commis­
sion. PPL acquired them in 1999 from its predecessor, the
Montana Power Company. 355 Mont., at 405–406, 229
P. 3d, at 426.
   PPL’s power facilities have existed at their locations for
many decades, some for over a century. See Robison,
supra, at 40 (Black Eagle Falls dam constructed by 1891).
Until recently, these facilities were operated without title­
based objection by the State of Montana. The State was
well aware of the facilities’ existence on the riverbeds—
indeed, various Montana state agencies had participated
in federal licensing proceedings for these hydroelectric
projects. See, e.g., Montana Power Co., 8 F. P. C. 751, 752
(1949) (Thompson Falls project); Montana Power Co., 27
FERC ¶62,097, pp. 63,188–63,189 (1984) (Ryan Dam of
8              PPL MONTANA, LLC v. MONTANA

                      Opinion of the Court

Missouri-Madison project). Yet the State did not seek, and
accordingly PPL and its predecessor did not pay, compen­
sation for use of the riverbeds. 355 Mont., at 406, 229
P. 3d, at 427. Instead, the understanding of PPL and the
United States is that PPL has been paying rents to the
United States for use of those riverbeds, as well as for use
of river uplands flooded by PPL’s projects. Reply Brief for
Petitioner 4; App. to Supp. Brief for Petitioner 4–5; Brief
for United States as Amicus Curiae 3, n. 3.
   In 2003, parents of Montana schoolchildren sued PPL in
the United States District Court for the District of Mon­
tana, arguing that PPL had built its facilities on riverbeds
that were state owned and part of Montana’s school trust
lands. 355 Mont., at 406, 229 P. 3d, at 426. Prompted
by the litigation, the State joined the lawsuit, for the first
time seeking rents for PPL’s riverbed use. The case was
dismissed in September 2005 for lack of diversity juris-
diction. Dolan v. PPL Montana, LLC, No. 9:03–cv–167
(D Mont., Sept. 27, 2005).
   PPL and two other power companies sued the State of
Montana in the First Judicial District Court of Montana,
arguing that the State was barred from seeking compensa­
tion for use of the riverbeds. 355 Mont., at 407–408, 229
P. 3d, at 427–428. By counterclaim, the State sought a
declaration that under the equal-footing doctrine it owns
the riverbeds used by PPL and can charge rent for their
use. Id., at 408, 229 P. 3d, at 428. The Montana trial
court granted summary judgment to Montana as to navi­
gability for purposes of determining riverbed title. Id., at
408–409, 413–414, 229 P. 3d, at 428, 431–432; App. to Pet.
for Cert. 143. The court decided that the State owned the
riverbeds. 355 Mont., at 428–429, 229 P. 3d, at 440. The
court ordered PPL to pay $40,956,180 in rent for use of
the riverbeds between 2000 and 2007. Id., at 431–432,
229 P. 3d, at 442–443. Whether a lease for future periods
would commence, and, if so, at what rental rate, seems to
                  Cite as: 565 U. S. ____ (2012)            9

                      Opinion of the Court

have been left to the discretion of the Montana Board of
Land Commissioners. App. to Pet. for Cert. 128–129.
   In a decision by a divided court, the Montana Supreme
Court affirmed. 355 Mont., at 461–462, 229 P. 3d, at 460–
461; id., at 462, 229 P. 3d, at 461 (dissenting opinion).
The court reasoned from the background principle that
“navigability for title purposes is very liberally construed.”
Id., at 438, 229 P. 3d, at 446. It dismissed as having
“limited applicability” this Court’s approach of assessing
the navigability of the disputed segment of the river ra­
ther than the river as a whole. Id., at 441–442, 229 P. 3d,
at 448–449. The Montana court accepted that certain
relevant stretches of the rivers were not navigable but
declared them “merely short interruptions” insufficient as
a matter of law to find nonnavigability, since traffic had
circumvented those stretches by overland portage. Id.,
at 438, 442, 229 P. 3d, at 446, 449. Placing extensive
reliance upon evidence of present-day use of the Madison
River, the court found that river navigable as a matter of
law at the time of statehood. Id., at 439, 229 P. 3d, at 447.
   Justice Rice dissented. Id., at 462, 229 P. 3d, at 461.
He stated that “courts are not to assume an entire river is
navigable merely because certain reaches of the river are
navigable.” Id., at 464, 229 P. 3d, at 462. The majority
erred, he wrote, in rejecting the “section-by-section ap­
proach” and “declaring, as a matter of law, that the
reaches claimed by PPL to be non-navigable are simply too
‘short’ to matter,” when in fact PPL’s evidence showed the
“disputed reaches of the rivers were, at the time of state­
hood, non-navigable.” Id., at 463–466, 476–477, 229 P. 3d,
at 462–464, 470.
   This Court granted certiorari, 564 U. S. ___ (2011), and
now reverses the judgment.
10            PPL MONTANA, LLC v. MONTANA

                      Opinion of the Court

                               III

                                A

   PPL contends the opinion of the Montana Supreme
Court is flawed in three respects: first, the court’s failure
to consider with care the navigability of the particular
river segments to which title is disputed, and its disregard
of the necessary overland portage around some of those
segments; second, its misplaced reliance upon evidence of
present-day, recreational use; and third, what the state
court itself called its liberal construction of the navigabil­
ity test, which did not place the burden of proof upon
the State to show navigability. Brief for Petitioner 26. The
United States as amicus is in substantial agreement with
PPL’s arguments, although it offers a more extended dis­
cussion with respect to evidence of present-day, recrea­
tional use. Brief for United States 27–33.
   It is appropriate to begin the analysis by discussing the
legal principles that control the case.
                             B
  The rule that the States, in their capacity as sovereigns,
hold title to the beds under navigable waters has origins
in English common law. See Shively v. Bowlby, 152 U. S.
1, 13 (1894). A distinction was made in England between
waters subject to the ebb and flow of the tide (royal rivers)
and nontidal waters (public highways). With respect to
royal rivers, the Crown was presumed to hold title to the
riverbed and soil, but the public retained the right of
passage and the right to fish in the stream. With respect
to public highways, as the name suggests, the public also
retained the right of water passage; but title to the riv­
erbed and soil, as a general matter, was held in private
ownership. Riparian landowners shared title, with each
owning from his side to the center thread of the stream, as
well as the exclusive right to fish there. See Idaho v.
Coeur d’Alene Tribe of Idaho, 521 U. S. 261, 285 (1997)
                  Cite as: 565 U. S. ____ (2012)            11

                      Opinion of the Court

(summarizing J. Angell, A Treatise on the Common Law
in Relation to Water-Courses 14–18 (1824)); 3 J. Kent,
Commentaries on American Law 528–529 (9th ed. 1858).
   While the tide-based distinction for bed title was the
initial rule in the 13 Colonies, after the Revolution Ameri­
can law moved to a different standard. Some state courts
came early to the conclusion that a State holds presump­
tive title to navigable waters whether or not the waters
are subject to the ebb and flow of the tide. See, e.g., Car-
son v. Blazer, 2 Binn. 475 (Pa. 1810); Executors of Cates v.
Wadlington, 12 S. C. L. 580 (1822); Wilson v. Forbes, 13
N. C. 30 (1828); Bullock v. Wilson, 2 Port. 436 (Ala. 1835);
Elder v. Burrus, 25 Tenn. 358 (1845). The tidal rule of
“navigability” for sovereign ownership of riverbeds, while
perhaps appropriate for England’s dominant coastal geog­
raphy, was ill suited to the United States with its vast
number of major inland rivers upon which navigation
could be sustained. See L. Houck, Law of Navigable Riv­
ers 26–27, 31–35 (1868); Packer v. Bird, 137 U. S. 661,
667–669 (1891). By the late 19th century, the Court had
recognized “the now prevailing doctrine” of state sovereign
“title in the soil of rivers really navigable.” Shively, supra,
at 31; see Barney v. Keokuk, 94 U. S. 324, 336 (1877) (“In
this country, as a general thing, all waters are deemed
navigable which are really so”). This title rule became
known as “navigability in fact.”
   The rule for state riverbed title assumed federal consti­
tutional significance under the equal-footing doctrine. In
1842, the Court declared that for the 13 original States,
the people of each State, based on principles of sovereign­
ty, “hold the absolute right to all their navigable waters
and the soils under them,” subject only to rights surren­
dered and powers granted by the Constitution to the
Federal Government. Martin v. Lessee of Waddell, 16 Pet.
367, 410 (1842). In a series of 19th-century cases, the
Court determined that the same principle applied to
12            PPL MONTANA, LLC v. MONTANA

                     Opinion of the Court

States later admitted to the Union, because the States in
the Union are coequal sovereigns under the Constitution.
See, e.g., Lessee of Pollard v. Hagan, 3 How. 212, 228–229
(1845); Knight v. United States Land Assn., 142 U. S. 161,
183 (1891); Shively, supra, at 26–31; see United States v.
Texas, 339 U. S. 707, 716 (1950). These precedents are the
basis for the equal-footing doctrine, under which a State’s
title to these lands was “conferred not by Congress but by
the Constitution itself.” Oregon ex rel. State Land Bd. v.
Corvallis Sand & Gravel Co., 429 U. S. 363, 374 (1977). It
follows that any ensuing questions of navigability for de-
termining state riverbed title are governed by federal
law. See, e.g., United States v. Utah, 283 U. S. 64, 75
(1931); United States v. Oregon, 295 U. S. 1, 14 (1935).
   The title consequences of the equal-footing doctrine can
be stated in summary form: Upon statehood, the State
gains title within its borders to the beds of waters then
navigable (or tidally influenced, see Phillips Petroleum Co.
v. Mississippi, 484 U. S. 469 (1988), although that is not
relevant in this case). It may allocate and govern those
lands according to state law subject only to “the para­
mount power of the United States to control such waters
for purposes of navigation in interstate and foreign com­
merce.” Oregon, supra, at 14; see Montana v. United
States, 450 U. S. 544, 551 (1981); United States v. Holt
State Bank, 270 U. S. 49, 54 (1926). The United States
retains any title vested in it before statehood to any land
beneath waters not then navigable (and not tidally influ­
enced), to be transferred or licensed if and as it chooses.
See Utah, supra, at 75; Oregon, supra, at 14.
   Returning to the “navigability in fact” rule, the Court
has explained the elements of this test. A basic formula­
tion of the rule was set forth in The Daniel Ball, 10 Wall.
557 (1871), a case concerning federal power to regulate
navigation:
                 Cite as: 565 U. S. ____ (2012)           13

                     Opinion of the Court

    “Those rivers must be regarded as public navigable
    rivers in law which are navigable in fact. And they
    are navigable in fact when they are used, or are sus­
    ceptible of being used, in their ordinary condition, as
    highways for commerce, over which trade and travel
    are or may be conducted in the customary modes of
    trade and travel on water.” Id., at 563.
   The Daniel Ball formulation has been invoked in con­
sidering the navigability of waters for purposes of as­
sessing federal regulatory authority under the Constitu­
tion, and the application of specific federal statutes, as to
the waters and their beds. See, e.g., ibid.; The Montello,
20 Wall. 430, 439 (1874); United States v. Appalachian
Elec. Power Co., 311 U. S. 377, 406, and n. 21 (1940) (Fed­
eral Power Act); Rapanos v. United States, 547 U. S. 715,
730–731 (2006) (plurality opinion) (Clean Water Act); id.,
at 761 (KENNEDY, J., concurring in judgment) (same). It
has been used as well to determine questions of title to
water beds under the equal-footing doctrine. See Utah,
supra, at 76; Oklahoma v. Texas, 258 U. S. 574, 586
(1922); Holt State Bank, supra, at 56. It should be noted,
however, that the test for navigability is not applied in the
same way in these distinct types of cases.
   Among the differences in application are the following.
For state title under the equal-footing doctrine, naviga­
bility is determined at the time of statehood, see Utah,
supra, at 75, and based on the “natural and ordinary con-
dition” of the water, see Oklahoma, supra, at 591. In
contrast, admiralty jurisdiction extends to water routes
made navigable even if not formerly so, see, e.g., Ex parte
Boyer, 109 U. S. 629, 631–632 (1884) (artificial canal); and
federal regulatory authority encompasses waters that only
recently have become navigable, see, e.g., Philadelphia Co.
v. Stimson, 223 U. S. 605, 634–635 (1912), were once
navigable but are no longer, see Economy Light & Power
14             PPL MONTANA, LLC v. MONTANA

                      Opinion of the Court

Co. v. United States, 256 U. S. 113, 123–124 (1921), or are
not navigable and never have been but may become so by
reasonable improvements, see Appalachian Elec. Power
Co., supra, at 407–408. With respect to the federal com­
merce power, the inquiry regarding navigation historically
focused on interstate commerce. See The Daniel Ball,
supra, at 564. And, of course, the commerce power ex­
tends beyond navigation. See Kaiser Aetna v. United
States, 444 U. S. 164, 173–174 (1979). In contrast, for title
purposes, the inquiry depends only on navigation and not
on interstate travel. See Utah, supra, at 76. This list of
differences is not exhaustive. Indeed, “[e]ach application
of [the Daniel Ball] test . . . is apt to uncover variations
and refinements which require further elaboration.” Ap-
palachian Elec. Power Co., supra, at 406.
                             IV 

                              A

  The primary flaw in the reasoning of the Montana Su­
preme Court lies in its treatment of the question of river
segments and overland portage.
  To determine title to a riverbed under the equal-footing
doctrine, this Court considers the river on a segment­
by-segment basis to assess whether the segment of the
river, under which the riverbed in dispute lies, is navigable
or not. In United States v. Utah, for example, the Court
noted,
     “the controversy relates only to the sections of the riv­
     ers which are described in the complaint, and the
     Master has limited his findings and conclusions as to
     navigability accordingly. The propriety of this course,
     in view of the physical characteristics of the streams,
     is apparent. Even where the navigability of a river,
     speaking generally, is a matter of common knowledge,
     and hence one of which judicial notice may be taken,
     it may yet be a question, to be determined upon evi­
                  Cite as: 565 U. S. ____ (2012)           15

                      Opinion of the Court

    dence, how far navigability extends.” 283 U. S., at 77.
The Court went on to conclude, after reciting and as­
sessing the evidence, that the Colorado River was naviga­
ble for its first roughly 4-mile stretch, nonnavigable for the
next roughly 36-mile stretch, and navigable for its remain­
ing 149 miles. Id., at 73–74, 79–81, 89. The Court noted
the importance of determining “the exact point at which
navigability may be deemed to end.” Id., at 90.
  Similarly, in Brewer-Elliott Oil & Gas Co. v. United
States, 260 U. S. 77, 85 (1922), the Court examined the
segment of the Arkansas River that ran along the Osage
Indian Reservation, assessing whether the Arkansas River
was “navigable in fact at the locus in quo.” The Court
concluded that the United States originally, and the Osag­
es as its grantees, unequivocally held title to the riverbeds
because the Arkansas River “is and was not navigable at
the place where the river bed lots, here in controversy,
are.” Id., at 86. The Court found the segment of river
along the reservation to be nonnavigable even though a
segment of the river that began further downstream was
navigable. Ibid. See also Oklahoma, supra, at 583, 584,
587–588, 589–591 (noting that “how far up the streams
navigability extended was not known”; assessing separate­
ly the segments of the Red River above and below its
confluence with the Washita River within Oklahoma’s
borders; and concluding that neither segment, and hence
“no part of the river within Oklahoma,” was navigable).
  The Montana Supreme Court discounted the segment­
by-segment approach of this Court’s cases, calling it
“a piecemeal classification of navigability—with some
stretches declared navigable, and others declared non­
navigable.” 355 Mont., at 440–442, 229 P. 3d, at 448–449.
This was error. The segment-by-segment approach to
navigability for title is well settled, and it should not be
disregarded. A key justification for sovereign ownership of
16            PPL MONTANA, LLC v. MONTANA

                      Opinion of the Court

navigable riverbeds is that a contrary rule would allow
private riverbed owners to erect improvements on the
riverbeds that could interfere with the public’s right to use
the waters as a highway for commerce. While the Federal
Government and States retain regulatory power to protect
public navigation, allocation to the State of the beds un­
derlying navigable rivers reduces the possibility of conflict
between private and public interests. See Utah, supra, at
82–83; Packer, 137 U. S., at 667. By contrast, segments
that are nonnavigable at the time of statehood are those
over which commerce could not then occur. Thus, there is
no reason that these segments also should be deemed
owned by the State under the equal-footing doctrine.
   Practical considerations also support segmentation.
Physical conditions that affect navigability often vary
significantly over the length of a river. This is particularly
true with longer rivers, which can traverse vastly different
terrain and the flow of which can be affected by varying
local climates. The Missouri River provides an excellent
example: Between its headwaters and mouth, it runs for
over 2,000 miles out of steep mountains, through canyons
and upon rocky beds, over waterfalls and rapids, and
across sandy plains, capturing runoff from snow melt and
farmland rains alike. These shifts in physical conditions
provide a means to determine appropriate start points and
end points for the segment in question. Topographical and
geographical indicators may assist. See, e.g., Utah, supra,
at 77–80 (gradient changes); Oklahoma, 258 U. S., at 589
(location of tributary providing additional flow).
   A segment approach to riverbed title allocation under
the equal-footing doctrine is consistent with the manner in
which private parties seek to establish riverbed title. For
centuries, where title to the riverbed was not in the sover­
eign, the common-law rule for allocating riverbed title
among riparian landowners involved apportionment de­
fined both by segment (each landowner owns bed and soil
                 Cite as: 565 U. S. ____ (2012)          17

                     Opinion of the Court

along the length of his land adjacent) and thread (each
landowner owns bed and soil to the center of the stream).
See J. Angell, A Treatise on the Law of Watercourses
18 (6th ed. 1869); Tyler v. Wilkinson, 24 F. Cas. 472, 474
(No. 14,312) (CC RI 1827) (Story, J.). Montana, moreover,
cannot suggest that segmentation is inadministrable when
the state courts managed to divide up and apportion the
underlying riverbeds for purposes of determining their
value and the corresponding rents owed by PPL.
  The Montana Supreme Court, relying upon Utah, de-
cided that the segment-by-segment approach is inapplicable
here because it “does not apply to ‘short interruption[s] of
navigability in a stream otherwise navigable.’ ” 355 Mont.,
at 442, 229 P. 3d, at 449 (quoting Utah, 283 U. S., at 77).
This was mistaken. In Utah, this Court noted in pass­
ing that the facts of the case concerned “long reaches
with particular characteristics of navigability or non­
navigability” rather than “short interruption[s].” Id., at
77. The Court in Utah did not say the case would have a
different outcome if a “short interruption” were concerned.
Ibid.
  Even if the law might find some nonnavigable segments
so minimal that they merit treatment as part of a longer,
navigable reach for purposes of title under the equal­
footing doctrine, it is doubtful that any of the segments in
this case would meet that standard, and one—the Great
Falls reach—certainly would not. As an initial matter, the
kinds of considerations that would define a de minimis
exception to the segment-by-segment approach would be
those related to principles of ownership and title, such as
inadministrability of parcels of exceedingly small size,
or worthlessness of the parcels due to overdivision. See
Heller, The Tragedy of the Anticommons, 111 Harv. L.
Rev. 621, 682–684 (1998) (explaining that dividing prop-
erty into square-inch parcels, could, absent countervail-
ing legal mechanisms, “paralyze the alienability of scarce
18            PPL MONTANA, LLC v. MONTANA

                     Opinion of the Court

resources . . . or diminish their value too drastically”). An
analysis of segmentation must be sensibly applied. A
comparison of the nonnavigable segment’s length to the
overall length of the stream, for instance, would be simply
irrelevant to the issue at hand.
   A number of the segments at issue here are both dis­
crete, as defined by physical features characteristic of
navigability or nonnavigability, and substantial, as a
matter of administrability for title purposes. This is best
illustrated by the Great Falls reach, which is 17 miles long
and has distinct drops including five waterfalls and con­
tinuous rapids in between. There is plenty of reason to
doubt that reach’s navigability based on the presence of
the series of falls. There is also reason to think that title
to that segment of bed would not be worthless or inadmin­
istrable. Indeed, the State sought and was awarded rent
in the amount of $41 million for PPL’s various hydroelec­
tric facilities attached to the riverbeds, half of which are
along the Great Falls reach.
   Applying its “short interruptions” approach, the Mon­
tana Supreme Court decided that the Great Falls reach
was navigable because it could be managed by way of land
route portage. 355 Mont., at 440, 442, 229 P. 3d, at 447,
449. The court noted in particular the portage of Lewis
and Clark’s expedition. Ibid. Yet that very portage re­
veals the problem with the Montana Supreme Court’s
analysis. Leaving behind their larger boats, Lewis and
Clark transported their supplies and some small canoes
about 18 miles over land, which took at least 11 days and
probably more. See Lewis and Clark Journals 126–152;
9 Journals of the Lewis & Clark Expedition 173; Dear
Brother 109. Even if portage were to take travelers only
one day, its significance is the same: it demonstrates the
need to bypass the river segment, all because that part of
the river is nonnavigable. Thus, the Montana Supreme
Court was wrong to state, with respect to the Great Falls
                  Cite as: 565 U. S. ____ (2012)           19

                      Opinion of the Court

reach and other stretches of the rivers in question, that
portages “are not sufficient to defeat a finding of navigabil­
ity.” 355 Mont., at 438, 229 P. 3d, at 446. In most cases,
they are, because they require transportation over land
rather than over the water. This is such a case, at least as
to the Great Falls reach.
   In reaching its conclusion that the necessity of portage
does not undermine navigability, the Montana Supreme
Court misapplied this Court’s decision in The Montello, 20
Wall. 430. See 355 Mont., at 438, 229 P. 3d, at 446. The
consideration of portage in The Montello was for a differ­
ent purpose. The Court did not seek to determine whether
the river in question was navigable for title purposes but
instead whether it was navigable for purposes of deter­
mining whether boats upon it could be regulated by the
Federal Government. 20 Wall., at 439, 445. The primary
focus in The Montello was not upon navigability in fact
but upon whether the river was a “navigable water of the
United States.” Id., at 439, 443. The latter inquiry is
doctrinally distinct. It turns upon whether the river
“forms by itself, or by its connection with other waters, a
continued highway over which commerce is, or may be,
carried with other States or foreign countries in the cus­
tomary modes in which such commerce is conducted by
water.” Id., at 439 (citing The Daniel Ball, 10 Wall. 557).
It is language similar to “continued highway” that Mon­
tana urges the Court to import into the title context in lieu
of the Court’s established segmentation approach. Brief
for Respondent 42–43, n. 16.
   The Montello reasonably concluded that the portages
required in that case did not prevent the river from being
part of a channel of interstate commerce. Portages con­
tinued that channel because goods could be successfully
transported interstate, in part upon the waters in ques­
tion. This provided sufficient basis to regulate steamboats
at places where those boats could and did, in fact, navigate
20             PPL MONTANA, LLC v. MONTANA

                      Opinion of the Court

portions of the river. 20 Wall., at 445. Here, by contrast,
the question regards ownership of the bed under river
segments that the Montana Supreme Court, by calling
them “interruptions in the navigation,” 355 Mont., at 442,
229 P. 3d, at 449, acknowledges were nonnavigable. The
reasoning and the inquiry of The Montello does not control
the outcome where the quite different concerns of the
riverbed title context apply.
   Having clarified that portages may defeat navigability
for title purposes, and do so with respect to the Great Falls
reach, the Court sees no evidence in the record that could
demonstrate that the Great Falls reach was navigable.
Montana does not dispute that overland portage was
necessary to traverse that reach. Indeed, the State admits
“the falls themselves were not passable by boat at state­
hood.” Brief for Respondent 10. And the trial court noted
the falls had never been navigated. App. to Pet. for
Cert. 137. Based on these statements, this Court now con­
cludes, contrary to the Montana Supreme Court’s decision,
that the 17-mile Great Falls reach, at least from the head
of the first waterfall to the foot of the last, is not navigable
for purposes of riverbed title under the equal-footing
doctrine.
   This Court also determines, based on evidence in the
record, that there is a significant likelihood that some of
the other river stretches in dispute also fail the federal
test of navigability for the purpose of determining title.
For example, as to the disputed segment of the Clark Fork
River, the Montana Supreme Court incorrectly stated the
sole evidence for nonnavigability “consists of conclusory
statements . . . without any specific factual support.” 355
Mont., at 440, 229 P. 3d, at 448. In fact, PPL introduced a
report of the U. S. Army Corps of Engineers from 1891,
two years after Montana’s date of statehood, documenting
that the portion of the Clark Fork river between Missoula
and Lake Pend Oreille (which includes the location of
                  Cite as: 565 U. S. ____ (2012)            21

                      Opinion of the Court

PPL’s Thompson Falls facility) had a fall of about 1,100
feet in 250 miles and “is a mountain torrential stream, full
of rocks, rapids, and falls, . . . utterly unnavigable, and in-
capable of being made navigable except at an enormous
cost.” 2 H. R. Exec. Doc., pt. 5, at 3250; see App. 379–380
(Docket No. 169). The report based its conclusions on
various failed attempts to navigate the river. It found the
Thompson Falls “a complete obstruction to navigation”
and the river around that area “exceedingly rapid, rough,
and full of rocks.” 2 H. R. Exec. Doc., pt. 5, at 3251. This
was consistent with a 1910 Federal District Court decree.
The decree adjudicated a title dispute between two private
parties over the riverbed near and under Thompson Falls
and declared the river at that place “was and is a non­
navigable stream incapable of carrying the products of
the country in the usual manner of water transportation.”
Steele v. Donlan, Equity No. 950 (CC D Mont., July 19,
1910), p. 1; see App. 380–381 (Docket No. 169). While the
ultimate decision as to this and the other disputed river
stretches is to be determined, in the first instance, by the
Montana courts upon remand, the relevant evidence
should be assessed in light of the principles discussed in
this opinion.
                             B
  The Montana Supreme Court further erred as a matter
of law in its reliance upon the evidence of present-day,
primarily recreational use of the Madison River. Error is
not inherent in a court’s consideration of such evidence,
but the evidence must be confined to that which shows the
river could sustain the kinds of commercial use that, as a
realistic matter, might have occurred at the time of state­
hood. Navigability must be assessed as of the time of
statehood, and it concerns the river’s usefulness for “ ‘trade
and travel,’ ” rather than for other purposes. See Utah,
283 U. S., at 75–76. Mere use by initial explorers or trap­
22            PPL MONTANA, LLC v. MONTANA

                     Opinion of the Court

pers, who may have dragged their boats in or alongside
the river despite its nonnavigability in order to avoid
getting lost, or to provide water for their horses and them­
selves, is not itself enough. See Oregon, 295 U. S., at
20–21 (evidence that “trappers appear to have waded or
walked” through the river, dragging their boats rather
than floating them, had “no bearing on navigability”).
   True, river segments are navigable not only if they
“[were] used,” but also if they “[were] susceptible of being
used,” as highways of commerce at the time of statehood.
Utah, supra, at 76 (internal quotation marks omitted).
Evidence of recreational use, depending on its nature, may
bear upon susceptibility of commercial use at the time of
statehood. See Appalachian Elec. Power Co., 311 U. S., at
416 (“[P]ersonal or private use by boats demonstrates the
availability of the stream for the simpler types of commer­
cial navigation”); Utah, 283 U. S., at 82 (fact that actual
use has “been more of a private nature than of a public,
commercial sort . . . cannot be regarded as controlling”).
Similarly, poststatehood evidence, depending on its na­
ture, may show susceptibility of use at the time of state­
hood. See id., at 82–83 (“[E]xtensive and continued
[historical] use for commercial purposes” may be the “most
persuasive” form of evidence, but the “crucial question” is
the potential for such use at the time of statehood, rather
than “the mere manner or extent of actual use”).
   Evidence of present-day use may be considered to the
extent it informs the historical determination whether the
river segment was susceptible of use for commercial navi­
gation at the time of statehood. For the susceptibility
analysis, it must be determined whether trade and travel
could have been conducted “in the customary modes of
trade and travel on water,” over the relevant river seg­
ment “in [its] natural and ordinary condition.” Id., at 76
(internal quotation marks omitted). At a minimum, there­
fore, the party seeking to use present-day evidence for title
                 Cite as: 565 U. S. ____ (2012)          23

                     Opinion of the Court

purposes must show: (1) the watercraft are meaningfully
similar to those in customary use for trade and travel
at the time of statehood; and (2) the river’s poststatehood
condition is not materially different from its physical con-
dition at statehood. See also Oregon, supra, at 18 (find-
ing that scientific and historical evidence showed that
the physical condition of particular water bodies had not
varied substantially since statehood in a way that might
affect navigation). If modern watercraft permit navigabil­
ity where the historical watercraft would not, or if the
river has changed in ways that substantially improve its
navigability, then the evidence of present-day use has
little or no bearing on navigability at statehood.
   The Montana Supreme Court opinion offered no indica­
tion that it made these necessary findings. The court
concluded the evidence of present-day use of the Madison
was probative of its susceptibility of use at statehood, but
there is no apparent basis for its conclusion. 355 Mont., at
442–443, 438–439, 229 P. 3d, at 449, 446–447. The court
did not find the watercraft similar to those used at the
time of statehood, and the State’s evidence of present-day
use for recreational fishing did not indicate what types of
boats are now used. App. 46–48. Modern recreational
fishing boats, including inflatable rafts and lightweight
canoes or kayaks, may be able to navigate waters much
more shallow or with rockier beds than the boats custom­
arily used for trade and travel at statehood.
   As to the river’s physical condition, the Montana Su­
preme Court did not assess with care PPL’s evidence
about changes to the river’s flow and the location and
pattern of its channel since statehood. The affidavit of
PPL’s expert in fluvial geomorphology—the study of river­
related landforms—at least suggests that as a result of
PPL’s dams, the river has become “less torrential” in high
flow periods and less shallow in low flow periods. App.
575–577 (Docket No. 170). Thus, the river may well be
24            PPL MONTANA, LLC v. MONTANA

                     Opinion of the Court

easier to navigate now than at statehood.
   The Montana Supreme Court altogether ignored the
expert’s reasoning about the past condition of the river’s
channels and the significance of that information for
navigability. Further, contrary to the Montana Supreme
Court’s suggestion, the expert’s affidavit was not mere
evidence of change in “seasonal variations” of water depth.
355 Mont., at 440, 229 P. 3d, at 448. It provided meaning­
ful evidence that the river’s conditions had changed since
statehood in ways that made present-day navigation of the
river easier in all seasons than it was at the relevant time.
While the Montana court was correct that a river need not
be susceptible of navigation at every point during the year,
neither can that susceptibility be so brief that it is not a
commercial reality. Against this background, the present­
day recreational use of the river did not bear on navigabil­
ity for purposes of title under the equal-footing doctrine.
The Montana Supreme Court’s reliance upon the State’s
evidence of present-day, recreational use, at least without
further inquiry, was wrong as a matter of law.
                           C
  The above analysis is sufficient to require reversal of
the grant of summary judgment to Montana. Therefore, the
Court declines to decide whether the Montana Supreme
Court further erred as to the burden of proof regarding
navigability.
                            D
  As a final contention, the State of Montana suggests
that denying the State title to the riverbeds here in dis­
pute will undermine the public trust doctrine, which con­
cerns public access to the waters above those beds for
purposes of navigation, fishing, and other recreational
uses. Brief for Respondent 20, 24–26. This suggestion
underscores the State’s misapprehension of the equal
                  Cite as: 565 U. S. ____ (2012)           25

                      Opinion of the Court

footing and public trust doctrines.
   The public trust doctrine is of ancient origin. Its roots
trace to Roman civil law and its principles can be found in
the English common law on public navigation and fishing
rights over tidal lands and in the state laws of this coun­
try. See Coeur d’Alene, 521 U. S., at 284–286; Illinois
Central R. Co. v. Illinois, 146 U. S. 387, 458 (1892);
D. Slade, Putting the Public Trust Doctrine to Work 3–8,
15–24 (1990); see, e.g., National Audubon Soc. v. Superior
Court of Alpine Cty., 33 Cal. 3d 419, 433–441, 658 P. 2d
709, 718–724 (1983); Arnold v. Mundy, 6 N. J. L. 1, 9–10
(1821). Unlike the equal-footing doctrine, however, which
is the constitutional foundation for the navigability rule of
riverbed title, the public trust doctrine remains a matter
of state law, see Coeur d’Alene, supra, at 285 (Illinois
Central, a Supreme Court public trust case, was “ ‘neces­
sarily a statement of Illinois law’ ”); Appleby v. City of New
York, 271 U. S. 364, 395 (1926) (same), subject as well to
the federal power to regulate vessels and navigation under
the Commerce Clause and admiralty power. While equal­
footing cases have noted that the State takes title to the
navigable waters and their beds in trust for the public, see
Shively, 152 U. S., at 49, 15–17, 24, 46, the contours of
that public trust do not depend upon the Constitution.
Under accepted principles of federalism, the States retain
residual power to determine the scope of the public trust
over waters within their borders, while federal law deter­
mines riverbed title under the equal-footing doctrine.
                             V
   As the litigation history of this case shows, Montana
filed its claim for riverbed rent over a century after the
first of the dams was built upon the riverbeds. Montana
had not sought compensation before then, despite its full
awareness of PPL’s hydroelectric projects and despite the
State’s own participation in the projects’ federal licensing
26            PPL MONTANA, LLC v. MONTANA

                     Opinion of the Court

process. While this Court does not reach the question, it
may be that by virtue of the State’s sovereignty, neither
laches nor estoppel could apply in a strict sense to bar the
State’s much belated claim. Still, the reliance by PPL and
its predecessors in title upon the State’s long failure to
assert title is some evidence to support the conclusion that
the river segments were nonnavigable for purposes of the
equal-footing doctrine.
   The Montana Supreme Court’s ruling that Montana
owns and may charge for use of riverbeds across the
State was based upon an infirm legal understanding of
this Court’s rules of navigability for title under the equal­
footing doctrine. As the Court said in Brewer-Elliott, “It is
not for a State by courts or legislature, in dealing with the
general subject of beds or streams, to adopt a retroactive
rule for determining navigability which . . . would enlarge
what actually passed to the State, at the time of her ad­
mission, under the constitutional rule of equality here
invoked.” 260 U. S., at 88.
                        *     *     *
  The judgment of the Montana Supreme Court is re­
versed, and the case is remanded for further proceedings
not inconsistent with this opinion.
                                          It is so ordered.
