## Facts

- Illinois (later joined by Michigan) alleged that Milwaukee-area municipal sewer systems discharged untreated and inadequately treated sewage into Lake Michigan, causing interstate pollution.
- In prior litigation, the Supreme Court recognized a federal common-law cause of action for interstate water pollution nuisance and directed the dispute to proceed in lower court.
- After Illinois filed in federal district court, Congress enacted the Federal Water Pollution Control Act Amendments of 1972 (Clean Water Act), creating a comprehensive EPA-centered regulatory and permitting system governing pollutant discharges into navigable waters.
- Milwaukee operated under discharge permits issued by the Wisconsin environmental agency; Wisconsin courts ordered compliance with permit limits and set a timetable for construction to address overflows.
- The federal district court nonetheless found a federal common-law nuisance and imposed effluent limits and construction requirements exceeding those in the permits and state-court order.
- The court of appeals held the Clean Water Act did not eliminate federal common-law nuisance, upheld relief as to overflows, and limited effluent restrictions to those consistent with permits and applicable federal regulations.

## Issues

1. Whether the Clean Water Act displaced federal common-law nuisance as a basis for interstate abatement actions targeting point-source discharges into navigable waters.
2. Whether federal courts may impose effluent limitations under federal common law that are more stringent than limitations set through the Act’s permitting and regulatory scheme.

## Decision

- The Supreme Court held that the Clean Water Act displaced the federal common law of interstate nuisance for point-source water pollution.
- Because Congress “spoke directly” through a comprehensive statutory program (including the NPDES permit system, effluent limitations, compliance timetables, and enforcement mechanisms), federal courts lacked authority to craft or apply separate federal common-law standards.
- The Court rejected the argument that the Act’s citizen-suit provision preserved an independent federal common-law nuisance remedy.
- The judgment was reversed insofar as it allowed federal common-law nuisance to remain available, and the case was remanded for proceedings governed by the statutory scheme.

## Legal Principles

- Federal common law is a limited, gap-filling doctrine and yields when Congress enacts legislation that directly addresses the subject previously governed by federal common law.
- Displacement of federal common law occurs when a federal statute provides a comprehensive framework that supplies the relevant standards and remedies; the statute, not federal common law, then governs.
- Under the Clean Water Act, point-source discharges are unlawful absent a permit, and applicable effluent limits and compliance obligations are set through the Act’s regulatory structure.
- Federal courts may not impose effluent limitations or abatement standards under federal common law that differ from or exceed those established under the Clean Water Act’s permitting and regulatory scheme.
- The decision concerns displacement of federal common law and does not itself resolve the availability of state-law remedies, which depend on separate analysis.

## Conclusion

The Supreme Court ruled that the Clean Water Act’s comprehensive permitting and enforcement regime displaced federal common-law nuisance for interstate point-source water pollution, requiring parties to proceed under the Act’s standards and remedies rather than judicially created federal nuisance rules.


City of Milwaukee v. Illinois, 451 U.S. 304 (1981)