The U.S. Supreme Court case State of Arizona v. State of California, et al., 1999 revolved around the dispute over water rights from the Colorado River among several Western states and Native American tribes. The court was asked to clarify a decree it had issued in 1964 that allocated specific amounts of river water to each state but did not address how much should go to Indian reservations within those states. In this decision, the court ruled that five Indian reservations along the river were entitled to enough water for their agricultural needs, which amounted to nearly one million acre-feet per year or about half of Arizona's total allotment under previous agreements. This ruling significantly impacted future negotiations and settlements regarding allocation and usage rights for this critical resource in an arid region.

In the dissenting opinion for the case of State of Arizona v. State of California, et al., 1999, it was argued that the majority's decision to allow California to divert more water from the Colorado River than previously agreed upon in a compact between several states was unjust and violated principles of federalism. The dissenters believed that by allowing this diversion without requiring any form of compensation or agreement from other affected states, particularly Arizona which had been relying on its share as per previous agreements, undermined interstate cooperation and trust. They also expressed concern over potential environmental impacts due to reduced river flows resulting from increased diversions by California. Furthermore, they disagreed with how much weight was given to historical usage patterns in determining water rights allocations rather than adhering strictly to terms set out in existing compacts among western states sharing Colorado River waters.