Arizona v. California

In a suit over Colorado River water allocation among several states, the United States intervened asserting water rights for five Indian reservations, arguing those rights were reserved when the reservations were created, including some created only by executive order; Arizona (plaintiff) argued the federal government lacked power to reserve such rights, that executive orders couldn't validly do so, and that any reserved water should be capped and equally apportioned between Arizona and the reservations.