## Facts

- Missouri filed an original action against Illinois and the Sanitary District of Chicago, an Illinois public corporation.
- The Sanitary District constructed and operated an artificial drainage channel to divert Chicago sewage away from Lake Michigan into the Des Plaines River, then the Illinois River, and ultimately the Mississippi River.
- Missouri alleged the Mississippi River is a public navigable stream and that many Missouri residents downstream of the Illinois River confluence relied on Mississippi River water for drinking and other domestic, agricultural, and industrial uses.
- Missouri claimed defendants’ diversion would carry large quantities of sewage and accumulated deposits into the Mississippi through an artificial and “unnatural” route, contaminating the water used in Missouri and injuring the riverbed within Missouri’s territory.
- Missouri did not challenge the canal as an unlawful structure or seek to prevent its use as a waterway; it sought to restrain the discharge and conveyance of sewage through the canal system into the Mississippi.
- Defendants filed a demurrer challenging both the Supreme Court’s jurisdiction and the legal sufficiency of the bill to warrant equitable relief.

## Issues

1. Whether the pleadings alleged a “controversy” within the Supreme Court’s original jurisdiction between Missouri and Illinois, and between Missouri and an out-of-state citizen (the Sanitary District).
2. Whether, assuming original jurisdiction, Missouri’s allegations were sufficient on their face to proceed in equity toward injunctive relief against alleged interstate pollution and public health harms.

## Decision

- The Supreme Court held the demurrer for want of jurisdiction could not be sustained because the bill alleged an interstate controversy within Article III original jurisdiction.
- The Court held the bill’s allegations, taken as true at the demurrer stage, were sufficient to proceed in equity.
- The demurrer was overruled, and defendants were required to appear and answer.
- The Court did not decide the ultimate merits of whether the canal actually caused the alleged harms.

## Legal Principles

- A state may invoke the Supreme Court’s original jurisdiction to seek relief against another state for alleged acts that threaten the complaining state’s health, territory, or use of interstate waters.
- At the pleading stage on demurrer, the Court accepts well-pleaded factual allegations as true and asks only whether they describe a cognizable controversy and a claim appropriate for equitable proceedings.
- A state’s asserted interest in protecting the health and welfare of its inhabitants and preventing injury within its territory can support an interstate controversy suitable for judicial resolution.
- A state-created public corporation of a defendant state may be joined when its operations are alleged to be the immediate cause of the complained-of interstate harm.

## Conclusion

The Court allowed Missouri’s interstate pollution suit to go forward by holding that the pleadings stated an original-jurisdiction controversy and an equitable claim sufficient to survive demurrer, requiring Illinois and the Sanitary District to answer without resolving the merits.


Missouri v. Illinois, 180 U.S. 208 (1901)