In the 1980 case Wisconsin et al. v. Illinois et al., the U.S. Supreme Court was asked to resolve a dispute between several states over water allocation from Lake Michigan and its connecting channels, specifically regarding diversions by the city of Chicago for municipal uses including waste disposal. The court had previously issued decrees in 1930 and 1967 limiting such diversions, but Illinois sought modifications to these restrictions due to changes in circumstances since they were imposed. The court found that while some modification might be warranted given improvements in sewage treatment technology and other factors, it would not completely lift the limitations as requested by Illinois because doing so could harm interests of other states bordering on Great Lakes waters who were also parties to this litigation. Instead, it appointed a Special Master with instructions to develop recommendations for possible adjustments based on current conditions and future needs of all concerned parties under principles of equitable apportionment - which requires balancing competing state interests fairly when dividing shared natural resources like interstate rivers or lakes.

In the dissenting opinion for Wisconsin et al. v. Illinois et al., Justice William Rehnquist disagreed with the majority's decision to grant a motion that would modify an existing decree concerning water diversion from Lake Michigan into the Chicago Waterway System. He argued that this modification was not justified by any significant changes in factual or legal conditions since the original decree, and thus should not have been granted according to principles of equity jurisprudence and federal common law governing modifications of consent decrees. Furthermore, he contended that granting such motions too easily could undermine stability and finality in judicial decisions, which are crucial values in our legal system.