## Facts

- Missouri filed an original bill in equity against Illinois and the Sanitary District of Chicago, alleging that operation of a drainage canal diverted Chicago sewage from Lake Michigan into the Des Plaines and Illinois Rivers and ultimately into the Mississippi River upstream of St. Louis.
- Missouri alleged the discharge materially polluted the Mississippi within Missouri, harmed public use of the river, and contributed to disease, including increased typhoid fever.
- Illinois and the Sanitary District denied that the canal caused downstream injury, contending the diverted flow improved the Illinois River’s quality and that downstream pollution and disease could be attributed to other sources, including sewage discharges by Missouri communities along the rivers.
- The case proceeded after an earlier ruling overruling a demurrer and emphasizing that any nuisance claim between states must be proved by determinate, satisfactory evidence and not be doubtful.
- After the canal began operating, Missouri filed a supplemental bill and introduced extensive expert and statistical evidence on water quality, bacteriology, and typhoid incidence.
- The record showed multiple potential pollution sources along the Missouri–Mississippi system, complicating proof that Chicago’s discharge was the cause of the alleged harms in Missouri.

## Issues

1. Whether the Supreme Court has original jurisdiction to adjudicate an interstate controversy alleging that one state’s authorized sewage-disposal activity creates a public nuisance in another state.
2. Whether Missouri proved, with the required clarity, that the drainage canal’s sewage discharge caused a public nuisance in Missouri, including material river pollution and disease.
3. Under what conditions the Court should grant equitable relief restraining one state’s activities at the suit of another state.

## Decision

- The Court held it had jurisdiction and authority to decide an interstate controversy alleging downstream injury from another state’s conduct.
- The Court denied relief on the merits, concluding Missouri did not clearly and fully prove that the canal’s operation caused the asserted pollution and resulting disease in Missouri.
- The Court emphasized the evidentiary uncertainty in attributing typhoid and water contamination over long distances given other substantial sources of sewage and contamination.
- The Court dismissed Missouri’s bill without prejudice, leaving open the possibility of a later action if stronger proof developed.

## Legal Principles

- The Supreme Court may hear interstate disputes in its original jurisdiction when one state alleges another state’s conduct creates a public nuisance affecting the complaining state.
- Equitable intervention between states requires a showing of serious magnitude and proof that is clear, determinate, and satisfactory; doubtful or speculative causation is insufficient.
- Even if a claim resembles a private nuisance action, the Court applies greater caution before restraining a sovereign state’s public works and resource use.
- When the evidence does not reliably isolate the defendant state’s conduct as the cause of the alleged injury, the Court may deny injunctive relief and dismiss without prejudice.

## Conclusion

The Court recognized its power to resolve interstate pollution controversies but dismissed Missouri’s nuisance claim because the evidence did not clearly establish that Chicago’s diverted sewage caused the alleged downstream pollution and disease in Missouri, preserving the option to refile if causation could later be shown with greater certainty.


Missouri v. Illinois, 200 U.S. 496 (1906)