Whether Federal Rule of Civil Procedure 19 requires dismissal of an action challenging a federal agency's use of water subject to state-adjudicated water rights if a Native American tribe asserts an interest in the suit and does not consent to joinder

QUESTION PRESENTED “[N]o problem” in the American West is “more critical than that of scarcity of water.” Colo. River Water Conservation Dist. v. United States, 424 U.S. 800, 804 (1976). To address this critical problem, Congress created an all-inclusive regime to ensure water is fairly allocated among all users claiming a right to water in a particular source. Under this regime, the responsibility to comprehensively adjudicate water rights falls to the States, which hold complex proceedings that often last decades and settle the rights of hundreds of users. These state adjudications include the federal government, whose sovereign immunity has been waived for that express purpose under the McCarran Amendment. 43 U.S.C. § 666(a). The United States’ waiver of sovereign immunity extends not just to its own water rights, but to reserved water rights the government holds on behalf of Native American tribes. Colo. River, 424 U.S. at 811. Given “the ubiquitous nature of Indian water rights” in the West, id., the Colorado River rule is a crucial feature of the state-federal water rights regime. The rule ensures all water rights in a water system can be adjudicated in a single proceeding, resulting in decrees that conclusively determine how much water each rights-holder can use and the priority of each right during shortages. The decision below tears a hole in this regime. Applying circuit precedent the United States itself believes to be incorrect and refuses to defend, the Ninth Circuit invented a rule under which one particular set of parties, Native American tribes, can ii veto any other water user’s attempt to vindicate stateadjudicated water rights against the federal government. According to the Ninth Circuit, Federal Rule of Civil Procedure 19 requires a tribe to be joined as an indispensable party in any suit against the federal government that implicates federal water rights held on behalf of the tribe. Yet because of tribal sovereign immunity, those suits cannot actually proceed absent the tribe’s consent. The result is that state-adjudicated water rights are meaningless against the federal government if any tribe objects. This is true even where, as here, the suit does not seek to prevent the United States from honoring tribal water rights, but only seeks to ensure that it does so consistent with the outcome of a decades-long water adjudication in which the United States itself was a party. Given the number of water sources in which tribes can claim an interest in the West, the Ninth Circuit’s rule will dominate water proceedings across this vast region, severely compromising the centuryold system for determining rights in the West’s scarcest and most important resource. The question presented is: Whether Federal Rule of Civil Procedure 19 requires dismissal of an action challenging a federal agency’s use of water subject to stateadjudicated water rights if a Native American tribe asserts an interest in the suit and does not consent to joinder.