The doctrine of reserved water rights. What are federal and tribal reserved water rights?

The doctrine of reserved water rights evolved to ensure that Indian reservations and public lands set aside by the federal government would have sufficient water to fulfill the purposes for which they were established. Whereas most western water rights (state-based appropriative rights) have a priority date based on when water was first put to beneficial use, federal reserved water rights have a priority date that goes back at least as far as the date on which the lands were set aside.

The reserved water rights doctrine is rooted in a number of judicial decisions, beginning with a U.S. Supreme Court decision that has come to be called the Winters Doctrine. The case of Winters vs United States involved a dispute between Native Americans of the Ft. Belknap Reservation and nonnative settlers over the use of the Milk River in Montana. When the water use of the settlers upstream from the reservation interfered with the Indians’ water need for large Irrigation diversions, the U.S. government filed a lawsuit on the reservation’s behalf.

The Winters decision held that when Congress created the Ft. Belknap Reservation, sufficient water to make the Indians a “pastoral and civilized People” was implicitly set aside. Therefore, although the normative settlers had perfected their water rights under Montana state law, the water right of the Indians of Ft. Belknap was prior, or senior in use.