(Slip Opinion)              OCTOBER TERM, 2017                                       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

                   TEXAS v. NEW MEXICO ET AL.

         ON EXCEPTIONS TO REPORT OF SPECIAL MASTER

    No. 141, Orig. Argued January 8, 2018—Decided March 5, 2018
To resolve their disputes over water rights in the Rio Grande, Colorado,
  New Mexico, and Texas, with Congress’s approval, signed the Rio
  Grande Compact. The Compact requires Colorado to deliver a speci-
  fied amount of water annually to New Mexico at the state line and
  directs New Mexico to deliver a specified amount of water to the Ele-
  phant Butte Reservoir. The Reservoir was completed in 1916 as part
  of the Federal Government’s Rio Grande Project and plays a central
  role in fulfilling the United States’s obligations to supply water under
  a 1906 treaty with Mexico as well as under several agreements with
  downstream water districts in New Mexico and Texas (Downstream
  Contracts).
     Texas brought this original action complaining that New Mexico
  has violated the Compact by allowing downstream New Mexico users
  to siphon off water below the Reservoir in ways not anticipated in the
  Downstream Contracts. The United States intervened and filed a
  complaint with parallel allegations. The Special Master filed a report
  recommending that the United States’s complaint be dismissed in
  part because the Compact does not confer on the United States the
  power to enforce its terms. This Court agreed to hear two exceptions
  to the report concerning the scope of the claims the United States can
  assert here: The United States says it may pursue claims for Com-
  pact violations; Colorado says the United States should be permitted
  to pursue claims only to the extent they arise under the 1906 treaty
  with Mexico.
Held: The United States may pursue the Compact claims it has pleaded
 in this original action. This Court, using its unique authority to mold
 original actions, see Kansas v. Nebraska, 574 U. S. ___, ___, has
 sometimes permitted the federal government to participate in com-
 pact suits to defend “distinctively federal interests” that a normal lit-
2                          TEXAS   v. NEW MEXICO

                                   Syllabus

    igant might not be permitted to pursue in traditional litigation, Mary-
    land v. Louisiana, 451 U. S. 725, 745, n. 21. While this permission
    should not be confused with license, several considerations taken col-
    lectively lead to the conclusion that the United States may pursue
    the particular claims it has pleaded in this case. First, the Compact
    is inextricably intertwined with the Rio Grande Project and the
    Downstream Contracts. Second, New Mexico has conceded in plead-
    ings and at oral argument that the United States plays an integral
    role in the Compact’s operation. Third, a breach of the Compact
    could jeopardize the federal government’s ability to satisfy its treaty
    obligations to Mexico. Fourth, the United States has asserted its
    Compact claims in an existing action brought by Texas, seeking sub-
    stantially the same relief and without that State’s objection. This
    case does not present the question whether the United States could
    initiate litigation to force a State to perform its obligations under the
    Compact or expand the scope of an existing controversy between
    States. Pp. 4–7.
United States’s exception sustained; all other exceptions overruled; and
 case remanded.

GORSUCH, J., delivered the opinion for a unanimous Court.
                        Cite as: 583 U. S. ____ (2018)                              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. 141, Orig.
                                   _________________


      STATE OF TEXAS, PLAINTIFF v. STATE OF

       NEW MEXICO AND STATE OF COLORADO 

       ON EXCEPTIONS TO REPORT OF SPECIAL MASTER
                                 [March 5, 2018]

   JUSTICE GORSUCH delivered the opinion of the Court.
   Will Rogers reportedly called the Rio Grande “the only
river I ever saw that needed irrigation.” In its long jour-
ney from the Colorado Rockies to the Gulf of Mexico, many
and sometimes competing demands are made on the riv-
er’s resources. In an effort to reconcile some of those
demands, Colorado, New Mexico, and Texas, acting with
the federal government’s assent, signed the Rio Grande
Compact in the 1930s. In today’s lawsuit, Texas claims
that New Mexico has defied the Compact. But at this
stage in the proceedings we face only a preliminary and
narrow question: May the United States, as an intervenor,
assert essentially the same claims Texas already has? We
believe it may.
   Like its namesake, the Rio Grande Compact took a long
and circuitous route to ratification. Its roots trace perhaps
to the 1890s, when Mexico complained to the United
States that increasing demands on the river upstream left
little for those below the border. The federal government
responded by proposing, among other things, to build a
reservoir and guarantee Mexico a regular and regulated
release of water. Eventually, the government identified a
2                  TEXAS v. NEW MEXICO

                     Opinion of the Court

potential dam site near Elephant Butte, New Mexico,
about 105 miles north of the Texas state line. The gov-
ernment presented this suggestion to representatives of
Mexico and the affected States in a 1904 “ ‘Irrigation Con-
gress,’ ” where it was “ ‘heartily endorse[d] and ap-
prove[d].’ ” Official Proceedings of the Twelfth National
Irrigation Congress 107 (G. Mitchell ed. 1905). So, in
1906, the United States agreed by treaty to deliver 60,000
acre-feet of water annually to Mexico upon completion of
the new reservoir. Convention Between the United States
and Mexico Providing for the Equitable Distribution of the
Waters of the Rio Grande for Irrigation Purposes, 34 Stat.
2953. After obtaining the necessary water rights, the
United States began construction of the dam in 1910 and
completed it in 1916 as part of a broader infrastructure
development known as the Rio Grande Project.
   But that still left the problem of resolving similar dis-
putes among the various States. After a number of interim
agreements and impasses, the affected parties eventu-
ally (and nearly simultaneously) negotiated several
agreements. And here again the Rio Grande Project and
its Elephant Butte Reservoir played a central role. In the
first set of agreements, the federal government promised
to supply water from the Reservoir to downstream water
districts with 155,000 irrigable acres in New Mexico and
Texas. In turn, the water districts agreed to pay charges
in proportion to the percentage of the total acres lying in
each State—roughly 57% for New Mexico and 43% for
Texas. We will call those agreements the “Downstream
Contracts.” Additionally, Colorado, New Mexico, and
Texas concluded the Rio Grande Compact, which Congress
approved in 1939. Act of May 31, 1939, 53 Stat. 785. In
the Compact, the parties indicated that nothing in their
agreement should be “construed as affecting” the federal
government’s treaty duties to deliver promised water to
Mexico, but only as resolving disputes among themselves.
                     Cite as: 583 U. S. ____ (2018)                   3

                         Opinion of the Court

Id., at 792. Toward that end, the Compact required Colo-
rado to deliver a specified amount of water annually to
New Mexico at the state line. Id., at 787–788. But then,
instead of similarly requiring New Mexico to deliver a
specified amount of water annually to the Texas state line,
the Compact directed New Mexico to deliver water to the
Reservoir. Id., at 788.* In isolation, this might have
seemed a curious choice, for a promise to deliver water to a
reservoir more than 100 miles inside New Mexico would
seemingly secure nothing for Texas. But the choice made
all the sense in the world in light of the simultaneously
negotiated Downstream Contracts that promised Texas
water districts a certain amount of water every year from
the Reservoir’s resources.
  Fast forward to this dispute. Texas filed an original
action before this Court complaining that New Mexico has
violated the Compact. According to Texas, New Mexico is
effectively breaching its Compact duty to deliver water to
the Reservoir by allowing downstream New Mexico users
to siphon off water below the Reservoir in ways the Down-
stream Contracts do not anticipate. After we permitted
the United States to intervene, it also filed a complaint
with allegations that parallel Texas’s. In response to
these complaints, New Mexico filed a motion to dismiss. A
Special Master we appointed to consider the case received
briefing, heard argument, and eventually issued an in-
terim report recommending that we deny New Mexico’s
motion to dismiss Texas’s complaint. We accepted that
recommendation. At the same time, the Master recom-
——————
  * To be precise, the Compact originally required New Mexico to deliver
water to a measuring station at San Marcial, New Mexico, upstream
of the Elephant Butte Reservoir. 53 Stat. 788. But the Compact also
established something called the Rio Grande Compact Commission and
gave it the power to administer the Compact in various ways. Id., at
791. In 1948, that Commission relocated the spot for measuring the
delivery obligation from the measuring station to the Reservoir itself.
4                  TEXAS v. NEW MEXICO

                      Opinion of the Court

mended that we dismiss in part the complaint filed by the
United States. The Master reasoned, in pertinent part,
that the Compact does not confer on the United States the
power to enforce its terms. In response to the Master’s
report, the parties filed a number of exceptions. We
agreed to hear two of these exceptions—one by the United
States and one by Colorado—concerning the scope of the
claims the United States can assert in this original action.
The United States says it may pursue claims for violations
of the Compact itself; Colorado says the United States
should be permitted to pursue claims only to the extent
they arise under the 1906 treaty with Mexico.
    Our analysis begins with the Constitution. Its Compact
Clause provides that “[n]o State shall, without the Con-
sent of Congress, . . . enter into any Agreement or Com-
pact with another State.” Art. I, §10, cl. 3. Congress’s
approval serves to “prevent any compact or agreement
between any two States, which might affect injuriously the
interests of the others.” Florida v. Georgia, 17 How. 478,
494 (1855). It also ensures that the Legislature can “check
any infringement of the rights of the national govern-
ment.” 3 J. Story, Commentaries on the Constitution of
the United States §1397, p. 272 (1833) (in subsequent
editions, §1403). So, for example, if a proposed interstate
agreement might lead to friction with a foreign country or
injure the interests of another region of our own, Congress
may withhold its approval. But once Congress gives its
consent, a compact between States—like any other federal
statute—becomes the law of the land. Texas v. New Mexico,
462 U. S. 554, 564 (1983).
    Our role in compact cases differs from our role in ordi-
nary litigation. The Constitution endows this Court with
original jurisdiction over disputes between the States. See
Art. III, §2. And this Court’s role in these cases is to serve
“ ‘as a substitute for the diplomatic settlement of contro-
versies between sovereigns and a possible resort to force.’ ”
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                     Opinion of the Court

Kansas v. Nebraska, 574 U. S. ___, ___ (2015) (slip op., at
6) (quoting North Dakota v. Minnesota, 263 U. S. 365,
372–373 (1923)). As a result, the Court may, “[i]n this
singular sphere, . . . ‘regulate and mould the process it
uses in such a manner as in its judgment will best pro-
mote the purposes of justice.’ ” 574 U. S., at ___–___ (slip
op., at 6–7) (quoting Kentucky v. Dennison, 24 How. 66, 98
(1861)).
   Using that special authority, we have sometimes per-
mitted the federal government to participate in compact
suits to defend “distinctively federal interests” that a
normal litigant might not be permitted to pursue in tradi-
tional litigation. Maryland v. Louisiana, 451 U. S. 725,
745, n. 21 (1981). At the same time, our permission
should not be confused for license. Viewed from some
sufficiently abstract level of generality, almost any com-
pact between the States will touch on some concern of the
national government—foreign affairs, interstate com-
merce, taxing and spending. No doubt that is the very
reason why the Constitution requires congressional ratifi-
cation of state compacts. But just because Congress en-
joys a special role in approving interstate agreements, it
does not necessarily follow that the United States has
blanket authority to intervene in cases concerning the
construction of those agreements.
   Still, bearing in mind our unique authority to mold
original actions, several considerations taken collectively
persuade us that the United States may pursue the par-
ticular claims it has pleaded in this case:
   First, the Compact is inextricably intertwined with the
Rio Grande Project and the Downstream Contracts. The
Compact indicates that its purpose is to “effec[t] an equi-
table apportionment” of “the waters of the Rio Grande”
between the affected States. 53 Stat. 785. Yet it can
achieve that purpose only because, by the time the Com-
pact was executed and enacted, the United States had
6                   TEXAS v. NEW MEXICO

                      Opinion of the Court

negotiated and approved the Downstream Contracts, in
which it assumed a legal responsibility to deliver a certain
amount of water to Texas. In this way, the United States
might be said to serve, through the Downstream Con-
tracts, as a sort of “ ‘agent’ of the Compact, charged with
assuring that the Compact’s equitable apportionment” to
Texas and part of New Mexico “is, in fact, made.” Texas’s
Reply to Exceptions to the First Interim Report of the
Special Master 40. Or by way of another rough analogy,
the Compact could be thought implicitly to incorporate the
Downstream Contracts by reference. Cf. 11 R. Lord, Wil-
liston on Contracts §30:26 (4th ed. 2017). However de-
scribed, it is clear enough that the federal government has
an interest in seeing that water is deposited in the Reser-
voir consistent with the Compact’s terms. That is what
allows the United States to meet its duties under the
Downstream Contracts, which are themselves essential to
the fulfillment of the Compact’s expressly stated purpose.
   Second, New Mexico has conceded that the United
States plays an integral role in the Compact’s operation.
Early in these proceedings, it argued that the federal
government was an indispensable party to this lawsuit
because it is “responsible for . . . delivery of . . . water” as
required by the Downstream Contracts and anticipated by
the Compact. Brief in Opposition 33; ibid. (“[T]he entry of
a Decree in accordance with Texas’ Prayer for Relief would
necessarily affect the United States’ interests in the [Rio
Grande] Project” contract). And at oral argument, New
Mexico contended that the federal government is so inte-
grally a part of the Compact’s operation that a State could
sue the United States under the Compact for interfering
with its operation. Tr. of Oral Arg. 59.
   Third, a breach of the Compact could jeopardize the
federal government’s ability to satisfy its treaty obliga-
tions. See Sanitary Dist. of Chicago v. United States, 266
U. S. 405, 423–425 (1925) (recognizing the strong interests
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                     Opinion of the Court

of the United States in preventing interference with its
treaty obligations). Our treaty with Mexico requires the
federal government to deliver 60,000 acre-feet of water
annually from the Elephant Butte Reservoir. And to fill
that Reservoir the Compact obliges New Mexico to deliver
a specified amount of water to the facility. So a failure by
New Mexico to meet its Compact obligations could directly
impair the federal government’s ability to perform its
obligations under the treaty. Now the Compact says
plainly that it may not be “construed as affecting the
obligations of the United States of America to Mexico”
under existing treaties. 53 Stat. 792. But that means
only that the Compact seeks to avoid impairing the federal
government’s treaty obligations. Permitting the United
States to proceed here will allow it to ensure that those
obligations are, in fact, honored.
   Fourth, the United States has asserted its Compact
claims in an existing action brought by Texas, seeking
substantially the same relief and without that State’s
objection. This case does not present the question whether
the United States could initiate litigation to force a State
to perform its obligations under the Compact or expand
the scope of an existing controversy between States.
   Taken together, we are persuaded these factors favor
allowing the United States to pursue the Compact claims
it has pleaded in this original action. Nothing in our
opinion should be taken to suggest whether a different
result would obtain in the absence of any of the considera-
tions we have outlined or in the presence of additional,
countervailing considerations. The United States’s excep-
tion is sustained, all other exceptions are overruled, and
the case is remanded to the Special Master for further
proceedings consistent with this opinion.

                                                  It is so ordered.
