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Reserved water rights case law

The decisions and statutes that define federal reserved water rights for tribal nations: the legal architecture every settlement in this index is built on. Citations verified against CourtListener or the issuing court's own site; each page links the primary record.

Case	Citation	Year	Court	Why it matters
Winters v. United States	207 U.S. 564	1908	Supreme Court of the United States	Origin of the federal reserved water rights (Winters) doctrine: tribal water rights arise by implication from the creation of the reservation itself, with a priority date as of its establishment.
McCarran Amendment (Suits for adjudication of water rights)	43 U.S.C. § 666	1952		The jurisdictional hinge of tribal water litigation: as construed in Colorado River (1976), it consents to state general-stream adjudications of federal and tribal reserved rights, which is where most tribal claims are quantified or settled.
Arizona v. California	373 U.S. 546	1963	Supreme Court of the United States	Established practicably irrigable acreage (PIA) as the quantification standard for tribal reserved water rights and confirmed that reservations created by Executive Order also carry reserved water.
Cappaert v. United States	426 U.S. 128	1976	Supreme Court of the United States	Confirmed that reserved rights are capped at the minimum necessary to fulfill the reservation's purpose while reaching hydrologically connected water, a bridge later cited in tribal groundwater litigation.
Colorado River Water Conservation District v. United States	424 U.S. 800	1976	Supreme Court of the United States	The 'Colorado River abstention' doctrine channels most tribal reserved-rights quantification into state general-stream adjudications rather than federal court.
United States v. New Mexico	438 U.S. 696	1978	Supreme Court of the United States	Imposed the primary-purposes limit on implied reserved rights, the framework against which tribal reservation purposes (and therefore tribal quantifications) are argued.
Wyoming v. United States (In re Big Horn River System adjudication)	492 U.S. 406	1989	Supreme Court of the United States	Left the Big Horn PIA-based quantification of the Wind River Reservation's reserved rights standing, but an equally divided affirmance sets no nationwide precedent.
Agua Caliente Band of Cahuilla Indians v. Coachella Valley Water District	849 F.3d 1262	2017	United States Court of Appeals for the Ninth Circuit	First federal appellate holding squarely extending tribal reserved water rights to groundwater, a pressure point for basins where surface supplies are fully appropriated.
Arizona v. Navajo Nation	599 U.S. 555	2023	Supreme Court of the United States	Reaffirms that Winters rights exist for the Navajo Reservation while foreclosing a treaty-based trust claim to force the United States to assess or develop water supplies, pushing tribes toward adjudication and settlement.