In the case of Arizona v. California et al., 1963, the Supreme Court was tasked with resolving a dispute over water rights from the Colorado River among several Western states and Mexico. The court ruled in favor of California, determining that it had greater rights to the river's water than Arizona due to its earlier development along the river and its reliance on this resource for agriculture and urban growth. This decision also affirmed an earlier decree by Congress known as Boulder Canyon Project Act (1928), which allocated specific amounts of water from Hoover Dam to each state involved in this dispute - namely, Nevada, New Mexico, Utah, Wyoming and Colorado alongside Arizona & California. Additionally, it recognized Mexican treaty rights to a portion of these waters under Treaty between United States & Mexico relating to Utilization of Waters of Colorado & Tijuana Rivers signed in 1944.

In the dissenting opinion for Arizona v. California et al., Justice Harlan disagreed with the majority's interpretation of the Boulder Canyon Project Act, arguing that it did not give the Secretary of Interior authority to contract water delivery without state approval. He believed this decision undermined states' rights and disrupted a long-standing balance between federal and state powers over water resources. Furthermore, he expressed concern about potential negative impacts on future interstate disputes regarding other natural resources if such broad power was given to a single federal official without clear congressional intent. He also criticized the court’s reliance on extrinsic evidence like legislative history in interpreting statutory language which he considered clear and unambiguous.