(Slip Opinion)              OCTOBER TERM, 2010                                       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

                   MONTANA v. WYOMING ET AL.

          ON EXCEPTION TO REPORT OF SPECIAL MASTER

    No. 137, Orig. Argued January 10, 2011—Decided May 2, 2011
Article V(A) of the Yellowstone River Compact ratified by Montana,
  Wyoming, and North Dakota provides: “Appropriative rights to the
  beneficial uses of the water of the Yellowstone River System existing
  in each signatory State as of January 1, 1950, shall continue to be en
  joyed in accordance with the laws governing the acquisition and use
  of water under the doctrine of appropriation.” 65 Stat. 666. Montana
  filed a bill of complaint, alleging that Wyoming breached Article V(A)
  by allowing its upstream pre-1950 water users to switch from flood to
  sprinkler irrigation, which increases crop consumption of water and
  decreases the volume of runoff and seepage returning to the river
  system. Thus, even if Wyoming’s pre-1950 users divert the same
  quantity of water as before, less water reaches downstream users in
  Montana. Concluding that the Compact permits more efficient irri
  gation systems so long as the conserved water is used to irrigate the
  same acreage watered in 1950, the Special Master found that Mon
  tana’s increased-efficiency allegation failed to state a claim. Montana
  has filed an exception.
Held: Because Article V(A) of the Compact incorporates the ordinary
 doctrine of appropriation without significant qualification, and be
 cause in Wyoming and Montana that doctrine allows appropriators to
 improve their irrigation systems, even to the detriment of down
 stream appropriators, Montana’s increased-efficiency allegation fails
 to state a claim for breach of the Compact under Article V(A). Pp. 4–
 19.
    (a) Background appropriation law principles do not support Mon
 tana’s position. The doctrine of appropriation provides that rights to
 water for irrigation are perfected and enforced in order of seniority,
 starting with the first person to divert water from a natural stream
 and apply it to a “beneficial use.” Once perfected, that water right is
2                       MONTANA v. WYOMING

                                  Syllabus

    senior to any later appropriators’ rights and may be fulfilled entirely
    before the junior appropriators get any water. However, junior ap
    propriators do acquire rights to the stream basically as it exists when
    they find it. Under this no-injury rule, junior users may, subject to
    the fulfillment of the senior users’ existing rights, prevent senior us
    ers from enlarging their rights to the junior users’ detriment. Here,
    the question is whether a switch to more efficient irrigation with less
    return flow is within Wyoming’s pre-1950 users’ existing appropriat
    ive rights or is an improper enlargement of that right. Although the
    law of return flows is an unclear area of appropriation doctrine, the
    Special Master correctly concluded that Wyoming’s pre-1950 users
    may switch to sprinkler irrigation. Pp. 4–16.
         (1) A change in irrigation methods does not appear to run afoul of
    the no-injury rule in Montana and Wyoming, which generally con
    cerns changes in the location of the diversion and the place or pur
    pose of use. Thus, an appropriator may increase his consumption by
    changing to a more water-intensive crop so long as he makes no
    change in acreage irrigated or amount of water diverted. Ordinary,
    day-to-day operational changes or repairs also do not violate the rule.
    Consumption can even be increased by adding farm acreage, if that
    was part of the plan from the start, and diligently pursued through
    the years. Irrigation system improvements seem to be the same sort
    of changes. This view is consistent with the fact that by 1950 both
    States had statutes regulating certain changes to water rights, but
    neither required farmers to take official action before adjusting irri
    gation methods. Cases in both States frequently describe the no
    injury rule as applying to changes in point of diversion, purpose of
    use, and place of use. The abundance of litigation over such
    changes—and the absence of any litigation over the sort of change at
    issue here—strongly implies that irrigation efficiency improvements
    were considered within the scope of the original appropriative right.
    Pp. 8–10.
         (2) The doctrine of recapture—which permits an appropriator
    who has diverted water for irrigation to recapture and reuse his own
    runoff and seepage before it escapes his control or his property—also
    supports treating irrigation efficiency improvements as within the
    original appropriative right. Montana and Wyoming cases appear to
    apply this basic doctrine without any qualification based on whether
    the return flow would re-enter the original stream or not. By using
    sprinklers instead of flood irrigation, Wyoming’s pre-1950 water us
    ers effectively recapture water. The sprinklers reduce loss from
    seepage and runoff and are simply different mechanisms for increas
    ing the volume of water available to crops without changing the
    amount of diversion. Pp. 10–15.
                       Cite as: 563 U. S. ____ (2011)                   3

                                 Syllabus

       (3) This conclusion is consistent with the view of water law
  scholars who have considered the question presented in this case.
  Pp. 15–16.
     (b) Also unpersuasive is Montana’s argument that, if background
  appropriation law principles do not support its position, Article V(A)’s
  “beneficial use” definition nonetheless restricts the scope of pre-1950
  appropriative rights to the net volume of water that was actually be
  ing consumed in 1950. Pp. 16–19.
       (1) “Beneficial use” is “that use by which the water supply of a
  drainage basin is depleted when usefully employed by the activities
  of man.” 65 Stat. 665. Montana contends that the term means the
  amount of depletion, and thus any activity increasing Wyoming’s pre
  1950 depletions beyond pre-1950 levels exceeds Article V(A)’s scope.
  Pp. 16–17.
       (2) Nothing in the Compact’s definition suggests such an inter
  pretation. A plain reading indicates that “beneficial use” is a type of
  use that depletes the water supply. This view is supported by the
  circumstances in the signatory States when the Compact was
  drafted. At that time, Wyoming had a statutory preference for irriga
  tion, a depletive use, over power generation, a nondepletive use. It
  thus it makes sense for the Compact to protect irrigation uses that
  were legislatively favored and represented the predominant use of
  the Yellowstone River system. Montana’s reading, by contrast, would
  drastically redefine the term. The amount of water put to “beneficial
  use” has never been defined by net water consumption. In irrigation,
  that amount has always included a measure of necessary loss, e.g.,
  runoff or evaporation. If the Compact’s definition were meant to
  drastically redefine “beneficial use,” this Court would expect far more
  clarity. Moreover, if the Compact effected a dramatic reframing of
  ordinary appropriation principles, the rest of Article V(A), which ex
  pressly states that “the laws governing the acquisition and use of wa
  ter under the doctrine of appropriation” control, would make little
  sense. Pp. 17–18.
       (3) If Article V(A) were intended to guarantee Montana a set
  quantity of water, it could have done so plainly, as done in other
  compacts, e.g., the Colorado River Compact of 1922. Pp. 18–19.
Exception overruled.

   THOMAS, J., delivered the opinion of the Court, in which ROBERTS,
C. J., and KENNEDY, GINSBURG, BREYER, ALITO, and SOTOMAYOR, JJ.,
joined. SCALIA, J., filed a dissenting opinion. KAGAN, J., took no part in
the consideration or decision of the case.
                       Cite as: 563 U. S. ____ (2011)                              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. 137, Orig.
                                  _________________


   STATE OF MONTANA, PLAINTIFF v. STATE OF

    WYOMING AND STATE OF NORTH DAKOTA 

  ON EXCEPTION TO THE REPORT OF THE SPECIAL MASTER
                                 [May 2, 2011]

   JUSTICE THOMAS delivered the opinion of the Court.
   This case arises out of a dispute between Montana and
Wyoming over the Yellowstone River Compact. Montana
alleges that Wyoming has breached Article V(A) of the
Compact by allowing its pre-1950 water appropriators to
increase their net water consumption by improving the
efficiency of their irrigation systems. The new systems,
Montana alleges, employ sprinklers that reduce the
amount of wastewater returned to the river, thus depriv­
ing Montana’s downstream pre-1950 appropriators of
water to which they are entitled. The Special Master has
filed a First Interim Report determining, as relevant here,
that Montana’s allegation fails to state a claim because
more efficient irrigation systems are permissible under the
Compact so long as the conserved water is used to irrigate
the same acreage watered in 1950. We agree with the
Special Master and overrule Montana’s exception to that
conclusion.
                            I
   From its headwaters in Wyoming, the Yellowstone River
flows nearly 700 miles northeast into Montana and then
North Dakota, where it joins the Missouri River. Several
2                  MONTANA v. WYOMING

                      Opinion of the Court

of its tributaries, including the Clarks Fork, Tongue,
Powder, and Bighorn Rivers, also begin in Wyoming and
cross into Montana before joining the main stem of the
Yellowstone River. This river system’s monthly and an­
nual flows, which are dictated largely by snow melt, vary
widely. In 1964, for example, the flow in the Tongue and
Powder Rivers was nearly 10 times the 1961 flow. App.
936. As the rivers came into heavy use for irrigation, it
became expedient to build water storage facilities for
preserving the heaviest flows. See First Interim Report of
Special Master 6 (hereinafter Report).
   Before funding new water storage facilities, Congress
sought agreement as to the allocation of the Yellowstone
River system among Wyoming, Montana, and North Da­
kota. In 1932, Congress granted the States permission to
negotiate a compact. See Act of June 14, 1932, ch. 253, 47
Stat. 306. Draft compacts were produced in 1935, 1942,
and 1944, but none was fully agreed upon. Finally, in
1951 Montana, Wyoming, and North Dakota ratified the
Yellowstone River Compact, and Congress consented to it.
Act of Oct. 30, 1951, 65 Stat. 663.
   The Yellowstone River Compact divides water into three
tiers of priority. First, Article V(A) provides: “Appropria­
tive rights to the beneficial uses of the water of the Yellow­
stone River System existing in each signatory State as of
January 1, 1950, shall continue to be enjoyed in accor­
dance with the laws governing the acquisition and use of
water under the doctrine of appropriation.” Id., at 666.
Second, Article V(B) allocates to each State the “quantity
of that water as shall be necessary to provide supplemen­
tal water supplies” for the pre-1950 uses protected by
Article V(A). Ibid. Third, “the remainder of the unused
and unappropriated water” of each tributary is divided by
percentage: Wyoming receives 60% of the remaining water
in the Clarks Fork River, 80% in the Bighorn River, 40%
in the Tongue River, and 42% in the Powder River; the
                     Cite as: 563 U. S. ____ (2011)                    3

                          Opinion of the Court

rest goes to Montana. Id., at 666–667.
   In February 2008, we granted Montana leave to file a
bill of complaint against Wyoming for breach of the Com­
pact. 552 U. S. 1175. Montana alleged that Wyoming had
breached the Compact by consuming more than its share
of the Tongue and Powder Rivers. Bill of Complaint 3,
¶8. Specifically, Montana claimed that Wyoming was ap­
propriating water for a number of new, post-1950 uses:
irrigating new acreage; building new storage facilities;
conducting new groundwater pumping; and increasing con­
sumption on existing agricultural acreage.1 Id., at 3–4,
¶¶ 9–12. According to Montana’s complaint, the Compact
did not permit Wyoming to use water for any of these
practices as long as Montana’s pre-1950 users’ rights
remained unfulfilled. Id., at 3, ¶8.
   In response, Wyoming filed a motion to dismiss the
complaint. We appointed a Special Master and referred
the motion to him. 555 U. S. __ (2008). After briefing and
argument, the Special Master recommended that we deny
Wyoming’s motion, because at least some of Montana’s
allegations state a claim for relief. The Special Master
found that “Article V of the Compact protects pre-1950
appropriations in Montana from new surface and ground­
water diversions in Wyoming, whether for direct use or for
storage, that prevent adequate water from reaching Mon­
tana to satisfy those pre-1950 appropriations.” Report 14–
15. But the Special Master agreed with Wyoming that
Montana’s allegations regarding “efficiency improvements
——————
  1 Montana   has since clarified that increased consumption on existing
acreage refers to the use of more efficient irrigation systems. The
“efficiency” of irrigation for our purposes refers to the amount of
wastewater that is lost, for example, to evaporation, seepage, runoff, or
deep percolation. Some of the lost water returns to the river and is
later available for downstream users. A more efficient irrigation
system loses less water; thus, though it may draw the same volume of
water from the river, net water consumption is increased.
4                     MONTANA v. WYOMING

                         Opinion of the Court

by pre-1950 appropriators in Wyoming” do not state a
claim for relief. Id., at 15. The States did not object to
most of the Special Master’s findings, and we have issued
orders accordingly. See 562 U. S. __ (2010); 562 U. S. __
(2010). Montana has filed an exception to the Special
Master’s rejection of its increased-efficiency allegation. It
is this exception that is before us.2
                              II
   Article V(A) of the Compact states that “[a]ppropriative
rights to the beneficial uses of [water] . . . existing in each
signatory State as of January 1, 1950, shall continue to be
enjoyed in accordance with the laws governing the acquisi­
tion and use of water under the doctrine of appropriation.”
Montana claims that its pre-1950 appropriators’ rights are
not “continu[ing] to be enjoyed” because upstream pre­
1950 appropriators in Wyoming have increased their
consumption by switching from flood to sprinkler irriga­
tion. Montana alleges that sprinkler systems increase
crop consumption of water and decrease the volume of
runoff and seepage that returns to the Tongue and Powder
rivers by 25% or more.3 See Montana’s Exception and
Brief 3 (hereinafter Brief for Montana). As a result, even
if Wyoming’s pre-1950 water users divert the same quan­
tity of water as before, less water reaches Montana. Ac­
cording to Montana, Article V(A) prohibits Wyoming from
allowing this practice when it deprives Montana’s pre­
——————
  2 Montana also raised an exception to the Special Master’s finding

that if Montana can remedy the shortage of water to its pre-1950 users
by curtailing its post-1950 uses without “prejudic[ing] Montana’s other
rights under the Compact,” then an intrastate remedy is “the appropri­
ate solution.” Report 15. We recommitted this exception to the Special
Master. 562 U. S. __ (2010).
  3 For purposes of resolving Wyoming’s motion to dismiss, we take as

true Montana’s allegation that the new sprinkler systems actually
reduce return flow to the rivers. Wyoming has not conceded that this is
true. See Wyoming’s Reply to Montana’s Exception 35, n. 6.
                     Cite as: 563 U. S. ____ (2011)                     5

                          Opinion of the Court

1950 users of their full water rights.
  The question, therefore, is whether Article V(A) allows
Wyoming’s pre-1950 water users—diverting the same
quantity of water for the same irrigation purpose and
acreage as before 1950—to increase their consumption of
water by improving their irrigation systems even if it
reduces the flow of water to Montana’s pre-1950 users.
Montana makes two basic arguments: that background
principles of appropriation law, to the extent they are
incorporated into the Compact, do not allow such an in­
crease in consumption; and that even if they do, the terms
of the Compact amended those principles in Montana’s
favor. The Special Master rejected these arguments, and
so do we.
                              A
   Because Article V(A) of the Compact protects
“[a]ppropriative rights to the beneficial uses of [water]” as
of 1950 “in accordance with the laws governing the ac-
quisition and use of water under the doctrine of appro­
priation,” we begin with an overview of appropriation
doctrine.4 As the Special Master explained, if “[a]p­
propriation law clearly proscribe[s] increases in consump­
tion on existing acreage to the detriment of downstream
appropriators, the Compact arguably would prohibit
Wyoming from allowing its appropriators to make
——————
  4 As  with all contracts, we interpret the Compact according to the
intent of the parties, here the signatory States. We thus look primarily
to the doctrine of appropriation in Wyoming and Montana, but, like the
States, we also look to Western water law more generally and authori­
ties from before and after 1950. The States appear to have assumed
that the doctrine has not changed in a way directly relevant here. We
therefore do not decide whether Article V(A) intended to freeze appro­
priation law as it stood in 1949, or whether it incorporates the evolution
of the doctrine over time, allowing Compact-protected rights to grow or
shrink accordingly. We resolve the matter of Montana’s exception
without prejudice to that issue. See Report 39–40.
6                  MONTANA v. WYOMING

                      Opinion of the Court

such increases to the detriment of Montana’s pre-1950
uses.” Report 65.
   As is typical west of the 100th meridian, the doctrine of
appropriation has governed water rights in Montana and
Wyoming since the 1800’s. See, e.g., Basey v. Gallagher,
20 Wall. 670, 683 (1875). As relevant here, the doctrine
provides that rights to water for irrigation are perfected
and enforced in order of seniority, starting with the first
person to divert water from a natural stream and apply it
to a beneficial use (or to begin such a project, if diligently
completed). See Hinderlider v. La Plata River & Cherry
Creek Ditch Co., 304 U. S. 92, 98 (1938); Arizona v. Cali
fornia, 298 U. S. 558, 565–566 (1936); Wyo. Const., Art. 8,
§3 (“Priority of appropriation for beneficial uses shall give
the better right”). The scope of the right is limited by the
concept of “beneficial use.” That concept restricts a farmer
“to the amount of water that is necessary to irrigate his
land by making a reasonable use of the water.” 1 C.
Kinney, Law of Irrigation and Water Rights §586, pp.
1007–1008 (2d ed. 1912) (hereinafter Kinney) (internal
quotation marks omitted); see also Bailey v. Tintinger, 45
Mont. 154, 176–178, 122 P. 575, 583 (1912); Quinn v. John
Whitaker Ranch Co., 54 Wyo. 367, 376–380, 92 P. 2d 568,
570–571 (1939). Once such a water right is perfected, it is
senior to any later appropriators’ rights and may be ful­
filled entirely before those junior appropriators get any
water at all.
   For our purposes, Montana’s pre-1950 water users are
similar to junior appropriators. As between the States,
the Compact assigned the same seniority level to all pre­
1950 water users in Montana and Wyoming. See Brief for
Montana 23; Brief for United States as Amicus Curiae 12.
But as Montana concedes, precisely because of this equal
seniority, its downstream pre-1950 users cannot stop
Wyoming’s upstream pre-1950 users from fully exercising
their water rights. Thus, when the rivers are low, Mon­
                  Cite as: 563 U. S. ____ (2011)            7

                      Opinion of the Court

tana’s downstream pre-1950 users might get no water at
all because the equally senior users upstream in Wyoming
may lawfully consume all of the water. Tr. of Oral Arg.
51.
   Junior appropriators are not completely without rights,
however. As they come online, appropriators acquire
rights to the stream basically as it exists when they find
it. See 2 Kinney §803, at 1403–1404. Accordingly, subject
to the fulfillment of all senior users’ existing rights, under
the no-injury rule junior users can prevent senior users
from enlarging their rights to the junior users’ detriment.
1 W. Hutchins, Water Rights Laws in the Nineteen West­
ern States 573 (1971) (hereinafter Hutchins).
   Montana’s pre-1950 users can therefore “insist that
[Wyoming’s pre-1950 users] confine themselves strictly
within the rights which the law gives them, that is, to the
amount of water within the extent of their appropriation
which they actually apply to some beneficial use.” 2
Kinney §784, at 1366. That general proposition is undis­
puted; the dispute here is in its application. Is a switch to
more efficient irrigation with less return flow within the
extent of Wyoming’s pre-1950 users’ existing appropriative
rights, or is it an improper enlargement of that right to
the detriment of Montana’s pre-1950 water users?
   As the Special Master observed, the law of return flows
is an unclear area of appropriation doctrine. Report 65
(citing Trelease, Reclamation Water Rights, 32 Rocky Mt.
L. Rev. 464, 469 (1960)). The States have not directed us
to any case on all fours with this one. Indeed, “[n]o west­
ern state court appears to have conclusively answered the
question.” Report 65.
   Despite the lack of clarity, the Special Master found
several reasons to conclude that Wyoming’s pre-1950 users
may switch to sprinkler irrigation. He found that the
scope of the original appropriative right includes such a
change so long as no additional water is diverted from the
8                      MONTANA v. WYOMING

                          Opinion of the Court

stream and the conserved water is used on the same acre­
age for the same agricultural purpose as before. We agree
with the Special Master.5
                             1
   First, although the no-injury rule prevents appropria­
tors from making certain water-right changes that would
harm other appropriators, a change in irrigation methods
does not appear to run afoul of that rule in Montana and
Wyoming. See id., at 69. Because each new appropriator
is entitled to the stream as it exists when he finds it, the
general rule is that “if a change in these conditions is
made by [a senior] appropriator, which interferes with the
flow of the water to the material injury of [the junior
appropriator’s] rights, he may justly complain.” 2 Kinney
§803, at 1404.
   But the no-injury rule is not absolute; it generally con­
cerns changes in the location of the diversion and the
place or purpose of use. Quigley v. McIntosh, 110 Mont.
——————
   5 The lack of clarity in this area of water law highlights the sensitive

nature of our inquiry and counsels caution. Our original jurisdiction
over cases between States brings us this dispute between Montana and
Wyoming about the meaning of their congressionally approved Yellow­
stone River Compact. See U. S. Const., Art. III, §2, cl. 2; 28 U. S. C.
§1251(a). Yet, because the Compact references and the parties direct
us to principles of appropriation doctrine, we find ourselves immersed
in state water law. See n. 4, supra. Our assessment of the scope of
these water rights is merely a federal court’s description of state law.
   The highest court of each State, of course, remains “the final arbiter
of what is state law.” West v. American Telephone & Telegraph Co., 311
U. S. 223, 236 (1940). We recognize that appropriation doctrine contin­
ues to evolve, and there are reasonable policy arguments in favor of
both States’ positions here. But it is not this Court’s role to guide the
development of state water regulation. See id., at 237 (“[I]t is the duty
of [federal courts] in every case to ascertain from all the available data
what the state law is and apply it rather than to prescribe a different
rule, however superior it may appear from the viewpoint of ‘general
law’ ”). Our decision is not intended to restrict the States’ determina­
tion of their respective appropriation doctrines.
                 Cite as: 563 U. S. ____ (2011)           9

                     Opinion of the Court

495, 505, 103 P. 2d 1067, 1072 (1940) (“[P]lace of diver­
sion, or place or purpose of use, may be changed only if
others are not thereby injured” (internal quotation marks
omitted)); see also 1 S. Wiel, Water Rights in the Western
States §498, p. 532 (3d ed. 1911) (hereinafter Wiel); Mont.
Code Ann. §89–803 (1947); Wyo. Stat. Ann. §41–3–104
(1977). Accordingly, certain types of changes can occur
even though they may harm downstream appropriators.
See D. Getches, Water Law in a Nutshell 175 (4th ed.
2009) (hereinafter Getches). For instance, an appropriator
may increase his consumption by changing to a more
water-intensive crop so long as he makes no change in
acreage irrigated or amount of water diverted. See id., at
183; East Bench Irrig. Co. v. Deseret Irrig. Co., 2 Utah 2d
170, 179, 271 P. 2d 449, 455 (1954) (assuming that farm­
ers may “legally increase the quantity of water consumed
in irrigating their lands by changing to more water con­
suming crops” and adding that “it would be difficult to
prevent . . . such increased consumptive use”). Ordinary,
day-to-day operational changes or repairs also do not
violate the no-injury rule. See, e.g., 1 Wiel §56, at 51
(“Would the fact that my pump has for years dripped
water onto a neighbor’s ground give him a right to say
that my pump must go on leaking?”). Consumption can
even be increased by adding farm acreage, so long as that
was part of the plan from the start, and diligently pursued
through the years. See Van Tassel Real Estate & Live
Stock Co. v. Cheyenne, 49 Wyo. 333, 357–359, 54 P. 2d 906,
913 (1936) (per curiam); 1 Hutchins 377–378; St. Onge v.
Blakely, 76 Mont. 1, 22–24, 245 P. 532, 539 (1926).
  Improvements to irrigation systems seem to be the sort
of changes that fall outside the no-injury rule as it exists
in Montana and Wyoming. Those changes are not to the
“place of diversion, or place or purpose of use,” Quigley,
supra, at 505, 103 P. 2d, at 1072, and thus seem to be
excluded, much like crop changes or day-to-day irrigation
10                    MONTANA v. WYOMING

                         Opinion of the Court

adjustments or repairs. This is also consistent with the
fact that by 1950 both States had statutes regulating
certain changes to water rights, but neither required
farmers to take official action before adjusting irrigation
methods.6 See Report 69–70, 87; id., at 69 (they “do not
generally have procedures for overseeing changes in water
efficiencies stemming from crop shifts or irrigation im­
provements where there are no formal changes in the
underlying water rights”). Like the Special Master, we
find this to be persuasive evidence that the States consid­
ered such changes permissible.
   Montana argues that, regardless of the statutes, private
lawsuits could be brought to challenge such efficiency
changes. But it has not provided a single example from
either State. Instead, Montana and Wyoming cases typi­
cally describe the no-injury rule as applying to changes in
point of diversion, purpose of use, and place of use. See,
e.g., Maclay v. Missoula Irrig. Dist., 90 Mont. 344, 355–
357, 3 P. 2d 286, 291 (1931); Thayer v. Rawlins, 594 P. 2d
951, 955 (Wyo. 1979). The abundance of litigation over
such changes—and the absence of any litigation over the
sort of change at issue here—strongly implies that irriga­
tion efficiency improvements do not violate the no-injury
rule and were considered within the scope of the original
appropriative right.
                            2
  The doctrine of recapture also supports treating im­
provements in irrigation efficiency as within the original
appropriative right. Under this doctrine, an appropriator
who has diverted water for irrigation purposes has the
right to recapture and reuse his own runoff and seepage
——————
  6 Mont. Code Ann. §89–803 (1947); Wyo. Stat. Ann. §71–401 (1945)
(water rights “cannot be detached from the lands, place or purpose for
which they are acquired” outside of specific exceptions); see also 1885
Mont. Laws p. 131, §3.
                     Cite as: 563 U. S. ____ (2011)                   11

                          Opinion of the Court

water before it escapes his control or his property.7 An
appropriator is entitled to the “exclusive control [of his
appropriated water] so long as he is able and willing to
apply it to beneficial uses, and such right extends to what
is commonly known as wastage from surface run-off and
deep percolation, necessarily incident to practical irriga­
tion.” Ide v. United States, 263 U. S. 497, 506 (1924)
(internal quotation marks omitted); see also Arizona Pub.
Serv. Co. v. Long, 160 Ariz. 429, 437–438, 773 P. 2d 988,
996–997 (1989) (“No appropriator can compel any other
appropriator to continue the waste of water which benefits
the former. If the senior appropriator, through scientific
and technical advances, can utilize his water so that none
is wasted, no other appropriator can complain”).
   Montana contends that this rule does not apply when
the runoff or seepage water would, if not recaptured,
return to the same stream from which it was originally
drawn. There is some support for Montana’s position—
that a beneficial user may not reuse water at all, even
while it is still on his property, if it otherwise would flow
back to the same stream—especially in Utah and Colorado
cases. See Deseret Irrig. Co., supra, at 180–182, 271 P. 2d,
at 456–457; Estate of Steed v. New Escalante Irrig. Co.,
846 P. 2d 1223, 1226 (Utah 1992); Comstock v. Ramsay, 55
Colo. 244, 252–258, 133 P. 1107, 1110–1111 (1913).8 But
other authorities draw no such exception based on where
the runoff or seepage is heading. See 2 Hutchins 580–582

——————
  7 And in some narrowly defined circumstances, he retains this right

even after the water leaves his property. See 1 Wiel §§38–40, at 37–43.
  8 Colorado has a relatively unique doctrine of recapture. See Hoese,

Comment, Recapture of Reclamation Project Ground Water, 53 Cal.
L. Rev. 541, 544, n. 18 (1965) (noting the general doctrine of recapture,
and adding that “[t]he Colorado rule, however, is to the contrary”);
United States v. Tilley, 124 F. 2d 850, 858 (CA8 1941) (allowing recap­
ture by the original appropriator under Nebraska law, and noting
Colorado’s opposite rule).
12                 MONTANA v. WYOMING

                     Opinion of the Court

(asserting that, even in Utah, “where the original appro­
priator retains possession and control of the waste and
seepage water from irrigation of his lands, he is entitled to
reuse these waters for his own benefit and need not return
them to the channel from which they were diverted” (em­
phasis added)); Getches 139–145; Woolman v. Garringer, 1
Mont. 535 (1872). And Montana cites no case from either
State here in which a court has recognized, much less
found controlling, the idea that a water user may not
reuse his own wastewater while it is still on his property
simply because it otherwise would return to the original
stream.
  In fact, Montana and Wyoming appear to apply, without
qualification, the basic doctrine that the original appro­
priator may freely recapture his used water while it re­
mains on his property and reuse it for the same purpose
on the same land. For example, in Binning v. Miller, 55
Wyo. 451, 102 P. 2d 54 (1940), a man was diverting water
from a creek fed largely by irrigation runoff and seepage
from Binning’s property. Although the court found that
the man had a right to that water once Binning’s runoff
and seepage had become a natural stream, it noted that
his right remained subject to Binning’s right “to use the
water above mentioned for beneficial purposes upon the
land for which the seepage water was [originally] appro­
priated.” Id., at 477, 102 P. 2d, at 63. In a later case, the
court explained that the man could not “secure a perma­
nent right to continue to receive the water” because
Binning “might find better ways of utilizing the water on
the same land so that less waste and seepage would oc­
cur.” Bower v. Big Horn Canal Assn., 77 Wyo. 80, 101, 307
P. 2d 593, 601 (1957).
  Similarly, in Bower v. Big Horn Canal Assn., the court
held that Bower could appropriate water as it seeped
across his property from the Big Horn Canal toward a
nearby river. Id., at 102–104, 307 P. 2d, at 602. The court
                 Cite as: 563 U. S. ____ (2011)          13

                     Opinion of the Court

added, however, that Bower’s right was subject always to
the Big Horn Canal’s right: “No appropriator can compel
any other appropriator to continue the waste of water
which benefits the former.” Id., at 101, 307 P. 2d, at 601.
Importantly, the court noted that “[i]f the senior appro­
priator by a different method of irrigation can so utilize
his water that it is all consumed in transpiration and
consumptive use and no waste water returns by seepage
or percolation to the river, no other appropriator can
complain.” Ibid.
  Finally, in Fuss v. Franks, 610 P. 2d 17 (Wyo. 1980),
water was seeping from Fuss’ property and into a pit in a
public right of way. Franks was the first to appropriate
the water from the pit. The court upheld Franks’ appro­
priation right because the water had already escaped from
Fuss’ property. The court said that the “owner of land
upon which seepage or waste water rises has the right to
use and reuse—capture and recapture—such waste wa­
ters,” but only before the water escapes his land, and “for
use only upon the land for which the water forming the
seepage was originally appropriated.” Id., at 20 (internal
quotation marks omitted). Fuss thus had no superior
right to the water that had left his property, and espe­
cially not for reuse on other lands.
  The law in Montana is similar. The Montana Supreme
Court has explained that “the general rule . . . is that the
owner of the right to use the water—his private property
while in his possession,—may collect it, recapture it, be­
fore it leaves his possession.” Rock Creek Ditch & Flume
Co. v. Miller, 93 Mont. 248, 268, 17 P. 2d 1074, 1080
(1933); see also A. Stone, Montana Water Law 66 (1994)
(noting that, according to the “early cases,” while “the
water is still seeping and running off one’s own land, the
landowner is free to recapture and further use it”).
  The right of recapture discussed in these authorities is
broad. As the Special Master recognized, the “language of
14                 MONTANA v. WYOMING

                      Opinion of the Court

the Wyoming Supreme Court . . . was expansive” in
Binning, Bower, and Fuss, and “all appear to hold that an
appropriator in Wyoming can increase his water use effi­
ciency by recovering runoff on his property or through
other means so long as the increased consumption is on
the same land to which the appropriative right attaches.”
Report 81; see also id., at 78–85; Thompson, Case Note,
Water Law—Reusing Irrigation Waste Water on Different
Lands: A Warning to Get a New Permit, Fuss v. Franks,
610 P. 2d 17 (Wyo. 1980), 16 Land & Water L. Rev. 71, 76
(1981) (concluding that in Wyoming, “a prior appropriator
can at anytime, utilize irrigation methods that are totally
consumptive, such as pumping the collected waste water
back to the top of the field or installing a sprinkler system,
thereby eliminating all waste of water”); Jones, Note,
Rights of the Original Appropriator to Recapture Water
Used in Irrigation, 11 Wyo. L. J. 39 (1956); Wille, Note,
The Right to Use Waste Water Before It Re-enters the
Stream, 12 Wyo. L. J. 47, 48 (1957).
  The Wyoming and Montana doctrine of recapture
strongly suggests that improvements in irrigation effi­
ciency are within the original appropriative right of Wyo­
ming’s pre-1950 water users. By using sprinklers rather
than flood irrigation, those water users effectively recap­
ture water. The sprinklers, by reducing loss due to seep­
age and runoff, operate much like, if more efficiently than,
cruder recapture systems involving ditches or pits. They
are simply different mechanisms for increasing the volume
of water available to the crops without changing the
amount of diversion. Binning, Bower, and Fuss expressly
acknowledged that in such situations, lower appropriators
who have perfected their own appropriative rights are
nonetheless at the mercy of the property owners from
which their water flows. See 55 Wyo., at 474–477, 102
P. 2d, at 63; 77 Wyo., at 100–104, 307 P. 2d, at 601–602;
610 P. 2d, at 20.
                 Cite as: 563 U. S. ____ (2011)          15

                     Opinion of the Court

                              3
   Our conclusion is consistent with that of water law
scholars who have considered the specific question pre­
sented in this case. One scholar asserted: “[O]f course,
increasing efficiency at one site may reduce the amount of
water available to downstream users who may rely on
return flows from other users. [Wyoming] law, however,
does not preclude more efficient uses merely because a
downstream user may be injured.” Squillace, A Critical
Look at Wyoming Water Law, 24 Land & Water L. Rev.
307, 331 (1989); see id., at 331, n. 156 (“For example, a
farmer who traditionally consumes only 50% of the water
applied to his land is free to change his crop or method of
applying water so as to increase his consumption to 60%”);
see also Thompson, supra, at 76 (“[A] prior appropriator
can at anytime . . . instal[l] a sprinkler system, thereby
eliminating all waste of water”). And a national hornbook
on water law has observed:
      “The rule allowing recapture and reuse of salvaged
    water on the original land can result in more water
    being consumed. For instance, if a water user is con­
    suming less than the permitted amount of water and
    plants a more water-intensive crop or puts in a more
    efficient irrigation system, most or all of the water
    that had previously been returned to the stream
    might be consumed. This can deprive other appro­
    priators of water on which they depend but it is al­
    lowed since it is technically within the terms of the
    original appropriation.” Getches 143–144.
Montana has not identified any scholars who have reached
the opposite conclusion.
  For all of these reasons, we hold that the doctrine of
appropriation in Wyoming and Montana allows appro­
priators to improve their irrigation systems, even to the
detriment of downstream appropriators. We readily ac­
16                 MONTANA v. WYOMING

                      Opinion of the Court

knowledge that this area of law is far from clear. See
supra, at 7. But the apparent scope of the no-injury rule
in Wyoming and Montana, the doctrine of recapture and
its broad reach in Wyoming and Montana case law, and
the specific conclusions of water law scholars all point in
the same direction, which also comports with the Special
Master’s exhaustive discussion and findings. Accordingly,
if Article V(A) simply incorporates background principles
of appropriation law, it allows Wyoming’s pre-1950 water
users to improve their irrigation efficiency, even to the
detriment of Montana’s pre-1950 users.
                              B
  Montana, however, takes another tack. It argues that
even if background principles of appropriation law do not
support its position, Article V(A) of the Compact does not
protect the full scope of ordinary appropriative rights.
Montana claims that the Compact’s definition of “benefi­
cial use” restricts the scope of protected pre-1950 appro­
priative rights to the net volume of water that was actu­
ally being consumed in 1950. We agree with the Special
Master that this argument also fails.
                               1
   Article V(A) protects “[a]ppropriative rights to the bene­
ficial uses of . . . water.” “Beneficial use,” in turn, is de­
fined in Article II(H) as “that use by which the water
supply of a drainage basin is depleted when usefully em­
ployed by the activities of man.” 65 Stat. 665. Montana
contends that “beneficial use” is thus defined as the
amount of depletion. According to Montana, any activity
that increases pre-1950 water users’ depletions in Wyo­
ming beyond pre-1950 levels exceeds the scope of the
appropriative rights that Article V(A) protects. See Brief
for Montana 25–28. On this basis, Montana asserts that
the Compact requires (subject to river conditions) that the
                 Cite as: 563 U. S. ____ (2011)           17

                     Opinion of the Court

same quantity of water that was reaching Montana as of
January 1, 1950, continue to do so. Id., at 26.
                              2
   We acknowledge that “beneficial use” refers to a type of
use that involves some depletion, as all irrigation does.
See Report 61. The part of the Compact’s definition of
“beneficial use” that refers to depletion—“that use by
which the water supply . . . is depleted”—is fairly clear. It
begins with “that use,” and the words that follow merely
explain that “that use” must be a use that “deplete[s]” the
“water supply.” Nothing in the language suggests that
“beneficial use” means a measure of the amount of water
depleted. A “beneficial use” within the meaning of the
Compact, therefore, is a type of use that depletes the water
supply.
   This plain reading makes sense in light of the circum­
stances existing in the signatory States when the Compact
was drafted. At that time, Wyoming had a statutory
preference for irrigation, a type of depletive use, over
power generation, a nondepletive use. Wyo. Stat. Ann.
§71–402 (1945). It makes sense that the Compact would
have been written to protect the irrigation uses that were
legislatively favored and represented the predominant use
of the Yellowstone River system. See Tr. of Oral Arg. 45–
47; 65 Stat. 663 (Compact Preamble) (noting that the
Compact recognizes “the great importance of water for
irrigation in the signatory States”).
   Montana’s reading of the Compact, by contrast, does not
follow from the text and would drastically redefine the
term “beneficial use” from its longstanding meaning. The
amount of water put to “beneficial use” has never been
defined by net water consumption. The quantity of water
“beneficially used” in irrigation, for example, has always
included some measure of necessary loss such as runoff,
evaporation, deep percolation, leakage, and seepage (re­
18                MONTANA v. WYOMING

                     Opinion of the Court

gardless of whether any of it returns to the stream). So,
water put to “[b]eneficial use is not what is actually con­
sumed, but what is actually necessary in good faith.” 1
Wiel §481, at 509; see also Trelease, The Concept of Rea­
sonable Beneficial Use in the Law of Surface Streams, 12
Wyo. L. J. 1, 10 (1957) (listing irrigation as a beneficial
use and noting that “the method of application, by flood­
ing, channeling, or sprinkling, is immaterial”); J. Sax, B.
Thompson, J. Leshy, & R. Adams, Legal Control of Water
Resources 131 (4th ed. 2006) (discussing normal irrigation
practices and observing that the amount of water put to
beneficial use “is often considerably more than the quan­
tum actually consumed”).
   If the Compact’s definition of “beneficial use” were
meant to drastically redefine the term into shorthand for
net water consumption, we would expect far more clarity.
For example, the Compact could have stated that it would
protect “only ‘the amount of water consumed for a benefi­
cial use in each signatory state as of January 1, 1950.’ ”
Report 60. Or it could have defined “beneficial use” as the
“volume by which the water supply . . . is depleted.” More­
over, if the Compact effected a dramatic reframing of
ordinary appropriation principles, the rest of Article V(A),
which expressly states that “the laws governing the acqui­
sition and use of water under the doctrine of appropria­
tion” control, would make little sense.
   We agree with the Special Master that the definition of
beneficial use in the Compact is unremarkable. Arti­
cle V(A) does not change the scope of the pre-1950 appro­
priative rights that it protects in both States.
                           3
  Finally, if Article V(A) were intended to guarantee
Montana a set quantity of water, it could have done so as
plainly as other compacts that do just that. By 1950,
Wyoming itself had entered into at least one compact that
                  Cite as: 563 U. S. ____ (2011)           19

                      Opinion of the Court

defined water rights in terms of depletion. The Colorado
River Compact of 1922 apportioned 7,500,000 acre-feet of
water per year for “the exclusive beneficial consumptive
use” of several upstream States, including Wyoming. That
compact specifically added that “[t]he States of the Upper
Division will not cause the flow of the river at Lee Ferry to
be depleted below an aggregate of 75,000,000 acre feet for
any period of ten consecutive years . . . .”        National
Resources Planning Bd., Water Resources Comm., Inter­
state Water Compacts, 1785–1941, p. 8 (1942). See also
Republican River Compact (1943), Kan. Stat. Ann.
§82a–518 (1997) (allocating water by the acre-foot for
beneficial consumptive use in Kansas, Nebraska, and
Colorado). And, even here in the Yellowstone River Com­
pact, Article V(B) unambiguously apportions the third tier
of Yellowstone River system water by percentage. 65 Stat.
666. The notion that Article V(A) accomplishes essen-
tially the same sort of depletive allocation with language
that has a different and longstanding meaning is simply
unpersuasive.
                          *    *    *
  We conclude that the plain terms of the Compact protect
ordinary “[a]ppropriative rights to the beneficial uses of
[water] . . . existing in each signatory State as of January
1, 1950.” Art. V(A), ibid. And the best evidence we have
shows that the doctrine of appropriation in Wyoming and
Montana allows appropriators to improve the efficiency of
their irrigation systems, even to the detriment of down­
stream appropriators. Montana’s allegation that Wyo­
ming has breached Article V(A) of the Compact by allow­
ing its pre-1950 water users to increase their irrigation
efficiency thus fails to state a claim. Accordingly, Mon­
tana’s first exception to the Special Master’s First Interim
Report is overruled.
                                             It is so ordered.
20              MONTANA v. WYOMING 


                  Opinion of the Court 



  JUSTICE KAGAN took no part in the consideration or
decision of this case.
                   Cite as: 563 U. S. ____ (2011)                1

                       SCALIA, J., dissenting

SUPREME COURT OF THE UNITED STATES
                           _________________

                           No. 137, Orig.
                           _________________


    STATE OF MONTANA, PLAINTIFF v. STATE OF

     WYOMING AND STATE OF NORTH DAKOTA 

  ON EXCEPTIONS TO THE REPORT OF THE SPECIAL MASTER
                           [May 2, 2011]

   JUSTICE SCALIA, dissenting.
   Thanks to improved irrigation techniques, Wyoming’s
farmers and cattlemen appear to consume more of the
water they divert from the Yellowstone River and its
tributaries today than they did 60 years ago—that is to
say, less of the diverted water ultimately finds its way
back into the Yellowstone. The Court interprets the Yel
lowstone River Compact (Compact), see Act of Oct. 30,
1951, ch. 629, 65 Stat. 663, to grant those Wyomans* the
right to increase their consumption so long as they do not
increase the volume of water they diverted beyond pre
1950 levels. Thus, it holds, Montana cannot complain that
the increased consumption interferes with its residents’
pre-1950 appropriative water rights. I disagree because
the Court’s analysis substitutes its none-too-confident
reading of the common law, see ante, at 7–8, and n. 5, for
the Compact’s definition of “beneficial use.”
   The doctrine of appropriation allocates perpetual water
rights along a river, on a “first in time[,] . . . superior in
right” basis, Wyoming v. Colorado, 259 U. S. 419, 459
(1922), to those who divert its flow and apply the water to
a beneficial use. See Hinderlider v. La Plata River &
——————
  * The dictionary-approved term is “Wyomingite,” which is also the
name of a type of lava, see Webster’s New International Dictionary
2961 (2d ed. 1957). I believe the people of Wyoming deserve better.
2                 MONTANA v. WYOMING

                     SCALIA, J., dissenting

Cherry Creek Ditch Co., 304 U. S. 92, 98 (1938). The
“beneficial use” requirement does most of the legal work.
It marks the types of uses that confer an appropriative
right—irrigation being a paradigmatic example, see
United States v. Willow River Power Co., 324 U. S. 499,
504, n. 2 (1945); and it “measure[s]” the extent of an ap
propriator’s claim, see Ide v. United States, 263 U. S. 497,
505 (1924); A. Tarlock, Law of Water Rights and Re
sources §§5:66, 5:68–5:69, pp. 5–130.3, 5–130.9 to 5–
130.10 (2010). At common law, an appropriator claims the
volume of water diverted and “reasonably required” by his
intended use. Id., §§5:65–5:66, at 5–127, 5–130.2; see
Quinn v. John Whitaker Ranch Co., 54 Wyo. 367, 377–378,
92 P. 2d 568, 570–571 (1939).
   The Compact borrows the concept of appropriation to
define the rights of pre-1950 water users along the Yel
lowstone River and its tributaries. Article V(A) promises
that “[a]ppropriative rights to the beneficial uses of the
water of the Yellowstone River System existing in each
signatory State as of January 1, 1950, shall continue to be
enjoyed in accordance with the laws governing the acquisi
tion and use of water under the doctrine of appropriation.”
65 Stat. 666. Article II(H) elaborates that a “Beneficial
Use” is one “by which the water supply of a drainage basin
is depleted when usefully employed by the activities of
man.” Id., at 665 (emphasis added).
   Like the common law, this definition lays out the types
of uses that qualify as beneficial and the volume of water
an appropriator may claim through his beneficial use. But
the Compact’s focus on whether a use depletes a river’s
water supply—not whether it diverts the river’s flow—
significantly limits the volume of water to which Wyoming
is entitled. For purposes of the Compact, Wyoming may
lay claim only to its beneficial users’ net consumption of
water, that is, the volume of water diverted from the river
minus the volume that flows (or seeps) back into the
                 Cite as: 563 U. S. ____ (2011)            3

                     SCALIA, J., dissenting

river’s channel.
   This interpretation, and only this interpretation, gives
meaning to the definition’s use of the word “depleted.” I
cannot write off as an accident the choice of this word
rather than the word consistently used elsewhere in the
Compact: “diverted.” See Sosa v. Alvarez-Machain, 542
U. S. 692, 711, n. 9 (2004). The Compact’s authors knew
how to use “diverted” and “diversion” when they wanted
to. Those two words appear repeatedly in other provisions
of the Compact, see Arts. II(G); V(B), (C); VII(A), (C), (D),
65 Stat. 665–668; and the Compact defines them in the
sentence immediately preceding the definition of “benefi
cial use.” See Art. II(G), id., at 665. But the Compact’s
authors chose to define beneficial use in terms of deple
tion—the first and only time the Compact uses any deriva
tive of the word “deplete.” It is in my view a clear indica
tion that the Compact intends to break from the common
law’s focus on diversion.
   The Court reduces the Compact’s deliberate use of “de
pleted” to an inconsequential slip of the pen. According to
today’s majority, Article II(H) speaks only to the types of
uses that confer appropriative rights. “Nothing in the
language,” it says, “suggests that ‘beneficial use’ means a
measure of the amount of water depleted.” Ante, at 17.
This is incomprehensible. On the Court’s own interpreta
tion “beneficial use” not only defines the types of uses that
confer appropriative rights, but also determines the vol
ume of water to which the rights attach—viz., only that
volume put to one of the specified types of uses. The only
question before us is whether “beneficial use” measures
the volume diverted or the volume depleted—and the
language of the Compact makes that clear.
   The Court provides no plausible explanation for use of
the word “depleted” instead of “diverted.” Its best effort
is the suggestion that the word was used to ensure that
hydroelectric power generation and other disfavored,
4                  MONTANA v. WYOMING

                     SCALIA, J., dissenting

nondepletive uses do not confer appropriative rights. See
ibid. That is highly unlikely, for two reasons. First, rely
ing on a subtle distinction between depletion and diversion
would be one of the clumsiest ways imaginable to accom
plish that simple goal, if it was not already accomplished
by other provisions of the Compact. One would instead
have expected the Compact simply to exclude the disfa
vored uses from the “usefu[l] . . . activities of man,”
Art. II(H), 65 Stat. 665, which confer appropriative rights.
Cf. Mont. Code Ann. §85–2–102(4) (2009) (listing types of
beneficial uses). Second, and even more conclusively,
hydroelectric generation, water wheels, and mill races—
the allegedly disfavored uses Wyoming and the United
States offer up to explain the word “depleted”—are already
excluded from appropriative rights (and probably from any
need for appropriative rights) by the Compact’s definition
of diversion: “the taking or removing of water from the
Yellowstone River or any tributary thereof when the water
so taken or removed is not returned directly into the
channel of the Yellowstone River or of the tributary from
which it is taken.” Art. II(G), 65 Stat. 665. The modifying
clause seems specifically designed to exclude hydroelectric
dams, water wheels and mill races, which, when they
divert water from the Yellowstone or its tributaries, “re
tur[n it] directly into the channel . . . from which it is
taken.”
  The Court objects to my interpretation because the word
“depleted” lacks the “clarity” necessary to “drastically
redefine the term ‘beneficial use’ from its longstanding
meaning,” ante, at 17. According to the Court, “[t]he
amount of water put to ‘beneficial use’ has never been
defined by net water consumption.” Ibid. Before making
this statement, the Court has spent some 10 pages, ante,
at 7–16, conducting a “sensitive . . . inquiry [that] counsels
caution”; into a field (state water law) where the answer of
this Court is not conclusive and hence not ipso facto cor
                  Cite as: 563 U. S. ____ (2011)             5

                      SCALIA, J., dissenting

rect (“it is not this Court’s role to guide”); resulting in the
Court’s best guess concerning “an unclear area of appro
priation doctrine”; answering a question which “ ‘[n]o
western state court [not even a lower court] appears to
have conclusively answered.’ ” Ante, at 7–8, and n. 5. The
Court calls that hitherto unanswered question “the law of
return flows,” ante, at 7, but it can more accurately be
described as the question whether the volume of water to
which an appropriator acquires rights is the entire volume
diverted for a beneficial use, or rather only the volume
depleted by the beneficial use. Which is to say that “bene
ficial use” has never had the “longstanding meaning” the
Court posits. If it has in the past been assumed to refer to
all water diverted from the stream rather than all water
depleted from the stream, that is only because the issue of
which of the two it means has never arisen. I find it quite
extraordinary that the Court should expend such heroic
efforts (imagine how many cases had to be read!) answer
ing a state water-law question that no court of any West
ern State has ever answered—a question that would cross
a Rabbi’s eyes—when the text in front of us provides
the clear answer insofar as this Compact is concerned:
“depleted.”
   The Court suggests that if the Compact’s authors
wanted to break from (what it considers) the common law,
they should have defined beneficial use as the “volume by
which the water supply . . . is depleted.” Ante, at 18 (in
ternal quotation marks omitted). That objection seems to
me to have little force when the Court cannot explain what
work “depleted” is supposed to do other than indicate
precisely the same concept more concisely. And the
Court’s helpful drafting tip proves that speaking with
greater clarity is not so easy. Following the Court’s advice
would make nonsense of Article V(B) of the Compact.
That provision allocates a fixed percentage “of the unused
and unappropriated water” of various tributaries to each
6                  MONTANA v. WYOMING

                     SCALIA, J., dissenting

State for post-1950 “storage or direct diversions for benefi
cial use on new lands or for other purposes.” 65 Stat. 666.
But if “beneficial use” in this last phrase means “the vol
ume of water by which . . . the water supply is depleted,”
the provision makes no sense. It would allocate a fixed
percentage of unused and unappropriated water for “a
volume of water by which the water supply is depleted.” It
makes perfect sense, of course, if “beneficial use” means all
uses that deplete the stream.
   The Court also wonders why, “if Article V(A) were in
tended to guarantee Montana a set quantity of water,” it
did not “d[o] so as plainly as other” interstate water com
pacts “that do just that.” Ante, at 18. This is a straw man.
Montana does not demand a precise volume of water each
year; nor does it insist that its pre-1950 water users al
ways receive enough water to satisfy their pre-1950 needs.
It merely asks that its pre-1950 water users occupy the
same position relative to Wyoming’s pre-1950 users in
2011 as they did in 1950—that whatever would have
flowed back into the Yellowstone after Wyoming appro
priators’ beneficial uses in 1950 if the river then had this
year’s flow, will also flow back this year. See Tr. of Oral
Arg. 13, 16, 24. In dry years, that may mean some Mon
tanans will have to make do with less or go without.
   Because I think the Court’s disposition disregards the
text of the Compact, I respectfully dissent.
