In the case of Arizona v. California et al., 1965, the Supreme Court was tasked with resolving a dispute over water rights to the Colorado River between several Western states and federal agencies. The court ruled in favor of California, upholding an earlier decree that allocated fixed amounts of water from the river to each state involved: Arizona, Nevada, New Mexico, Utah and Wyoming. This decision also affirmed that Indian reservations along the river were entitled to sufficient water for irrigation purposes under federal law - a significant victory for Native American tribes in these regions. Furthermore, it clarified that contracts made by Secretary of Interior regarding delivery or storage services did not infrive upon any state's apportioned share unless explicitly stated otherwise.

In the dissenting opinion for Arizona v. California et al., Justice Harlan, joined by Justices Stewart and Clark, disagreed with the majority's interpretation of the Boulder Canyon Project Act (BCPA). They argued that Congress did not intend to allocate water rights among seven states but rather sought to facilitate a compact between them. The dissenters believed that in absence of such a compact, it was inappropriate for the Supreme Court to determine water allocations unilaterally. Additionally, they contended that even if Congress had intended BCPA as an apportionment scheme, its terms were ambiguous and should be interpreted narrowly so as not to infringe upon state sovereignty over water resources within their borders. Furthermore, they criticized the majority's reliance on Secretary of Interior’s reports which were never formally approved by Congress or subjected to judicial review.