## Facts

- Wyoming initiated a comprehensive, system-wide adjudication of all water rights in the Big Horn River system in state court under the McCarran Amendment, joining the United States (as tribal trustee and federal landowner), the Shoshone and Arapaho Tribes, and non-Indian water users.
- Phase I of the adjudication addressed federal reserved water rights for the Wind River Reservation, established by the Treaty of 1868.
- A special master recommended treating the reservation’s purpose as an Indian “homeland,” supporting reserved rights for irrigation and additional uses (including fisheries, wildlife, aesthetics, and mineral/industrial and municipal needs).
- The water judge rejected the “homeland” approach and quantified the tribes’ reserved right as the water necessary to irrigate all practicably irrigable acreage (PIA) on the reservation, recognizing irrigation (and associated stock watering) but not separate reserved rights for other categories of use.
- Multiple parties appealed, and the Wyoming Supreme Court largely affirmed the water judge’s Phase I determination.

## Issues

1. What was the Wind River Reservation’s primary purpose under the 1868 treaty for purposes of federal reserved water rights: a narrowly agricultural purpose or a broader homeland purpose?
2. Whether reserved rights must be quantified solely by the PIA standard for irrigation, or may include distinct reserved rights for non-irrigation uses (e.g., fisheries, wildlife, aesthetics, mineral/industrial, and municipal uses).
3. How federal reserved rights should be integrated into Wyoming’s prior appropriation system within a state-court general stream adjudication.

## Decision

- The Wyoming Supreme Court held that the reservation’s primary purpose, as relevant to implied reserved rights, was agricultural rather than a generalized homeland purpose.
- The court adopted and applied the PIA standard to quantify the tribes’ reserved right for irrigation, consistent with federal precedent approving PIA as a quantification method for tribal irrigation rights.
- The court declined to recognize separate reserved rights for fisheries, wildlife, aesthetics, or mineral/industrial development, reasoning those uses were not within the reservation’s primary purpose for implied reservation, and could be pursued through state-law appropriations.
- The U.S. Supreme Court affirmed the judgment by an equally divided Court, leaving the state court’s result in place and limiting review to the quantification standard.

## Legal Principles

- Federal reserved water rights arise by implication when the United States withdraws land for a federal reservation, reserving water necessary to accomplish the reservation’s primary purposes, with priority dating to the reservation’s creation.
- Under a narrow primary-purpose approach, reserved rights are limited to what is necessary for the reservation’s primary purposes; water for secondary purposes is not impliedly reserved if it can be obtained under state law.
- For tribal reserved rights tied to irrigation, quantification may be based on practicably irrigable acreage: lands that can feasibly and economically be irrigated using reasonable means.
- A state court may adjudicate Indian reserved water rights in a comprehensive stream adjudication under the McCarran Amendment, and then integrate quantified federal rights into the state’s administration of priorities, while recognizing their federal character and seniority.

## Conclusion

The Wyoming Supreme Court confined the Wind River Reservation’s implied reserved water right to a PIA-quantified irrigation right (including associated stock watering) and rejected distinct reserved rights for environmental and industrial categories, leaving those non-irrigation needs to be met through Wyoming’s prior appropriation system; the U.S. Supreme Court’s equally divided affirmance left that judgment intact.


In re Gen. Adjudication of All Rights to Use Water in the Big Horn River Sys., 753 P.2d 76 (Wyo. 1988), aff’d sub nom. Wyoming v. United States, 492 U.S. 406 (1989)