## Facts

- The Pyramid Lake Indian Reservation in Nevada depends on Truckee River inflows to support Pyramid Lake and its fisheries.
- The federal Newlands Reclamation Project diverted Truckee River water for irrigation near Fallon, Nevada, reducing flows into Pyramid Lake.
- In 1913, the United States filed a federal suit to adjudicate Truckee River water rights for the benefit of both the Reservation and the Newlands Project, naming Nevada water users as defendants.
- The litigation ended in a 1944 decree, entered pursuant to settlement, which quantified Truckee River rights for the Reservation (based on reserved-rights doctrine) and for the Newlands Project (then operated by the Truckee–Carson Irrigation District).
- In 1973, the United States filed a new federal action seeking additional Truckee River rights for the Reservation, asserting that the earlier decree addressed only irrigation needs and that further water was reserved to preserve the lake and fisheries.
- Defendants asserted res judicata, arguing that the 1944 decree conclusively determined the Reservation’s Truckee River rights and barred relitigation.
- The district court dismissed on claim-preclusion grounds.
- The court of appeals held the earlier decree preclusive as between the United States/Tribe and the original defendants and successors, but allowed litigation to proceed regarding allocations between the Tribe and certain Newlands Project landowners based on the theory that the United States had represented both and had not made them formally adverse.

## Issues

1. Whether claim preclusion bars the United States and the Tribe from seeking additional Truckee River water for the Reservation beyond the rights quantified in the 1944 decree.
2. Whether the Tribe and Newlands Project landowners (and successors) are bound inter se by the prior decree despite both being represented by the United States in the earlier adjudication.
3. Whether changing the asserted purpose for the Reservation’s water (from irrigation to lake and fishery preservation) creates a different cause of action avoiding claim preclusion.

## Decision

- The Supreme Court held that res judicata bars the United States and the Tribe from relitigating and enlarging the Reservation’s Truckee River rights beyond the 1944 decree.
- The Court rejected the view that the Government could reallocate a single federal entitlement between the Reservation and the reclamation project; Project landowners held the beneficial interest in the project water rights confirmed in the earlier decree.
- The Court concluded that the later suit asserted the same claim to Truckee River water for the same Reservation; a different asserted use did not create a new cause of action.
- The Court held that the Tribe was in privity with the United States, which represented the Tribe in the earlier case, and that the Tribe’s reserved right had been pleaded and quantified in the decree.
- The Court rejected any requirement that the Tribe and Project landowners had to be “strictly adverse” in the earlier comprehensive adjudication for the decree to bind their rights.
- The Court reversed the court of appeals to the extent it allowed further litigation and left the 1944 decree conclusive as to Truckee River rights between the United States (including the Tribe) and Truckee River appropriators and successors.

## Legal Principles

- A final decree in a comprehensive water-rights adjudication has ordinary claim-preclusive effect against the United States and tribal interests the United States represented, when the same claim and privity requirements are satisfied.
- For reserved-rights claims, once the United States litigates and a decree quantifies the reservation’s rights, later efforts to obtain additional water for the same reservation are barred as the same cause of action.
- In federal reclamation projects, the United States may hold legal title or act in a fiduciary capacity, but the beneficial interest in project water rights resides in the individual landowners; the Government cannot later treat those rights as a reassignable federal pool.
- In multiparty river adjudications, preclusion does not depend on a formalized showing of strict adversity among all interests represented in the earlier proceeding.
- Finality interests are especially weighty in western water adjudications; reopening settled allocations decades later is disfavored because it destabilizes established rights.

## Conclusion

The Court enforced claim preclusion to prevent the United States and the Tribe from reopening a settled Truckee River adjudication to seek additional reserved water for lake and fishery preservation, holding that the 1944 decree conclusively fixed the Reservation’s rights and bound the Tribe and reclamation-project landowners and successors despite the Government’s prior representation of multiple interests.


Nevada v. United States, 463 U.S. 110 (1983)