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Wisconsin v. Illinois, 278 U.S. 367 (1929)

Why this matters: Wisconsin sued Chicago for draining Lake Michigan and won. The Supreme Court has been supervising that diversiondiversionMoving water out of the Great Lakes basin. The Compact bans new ones except in a few narrow cases. ever since. This is the original Great Lakes water fight, and it’s the reason the region treats diversiondiversionMoving water out of the Great Lakes basin. The Compact bans new ones except in a few narrow cases. as an existential issue rather than a technical one.

Doctrine: Interstate water disputes, Great Lakes diversion

Case name and citation

Wisconsin v. Illinois, 278 U.S. 367 (1929). Decided together with Michigan v. Illinois and New York v. Illinois.

Court and year

Supreme Court of the United States, original jurisdiction. Decided January 14, 1929. Charles Evans Hughes served as Special Master.

One-line holding

The Sanitary District of Chicago’s diversion from Lake Michigan far exceeded what navigation required and was unlawful to that extent, and Illinois had to reduce it.

Facts

Chicago had reversed the Chicago River. Rather than send its sewage into Lake Michigan, which was also its drinking water, the city dug a canal and sent the river the other way, toward the Mississippi.

Making that work required pulling enormous volumes of lake water into the canal to dilute and carry the sewage. By the 1920s the Sanitary District was diverting an annual average of 8,500 cubic feet per secondcubic feet per secondA flow rate rather than a volume. 1 cubic foot per second running all day is about 2 acre-feet., under a permit the Secretary of War enlarged on March 3, 1925.

Wisconsin filed an original bill in the Supreme Court on July 14, 1922. Minnesota, Ohio, and Pennsylvania joined as co-complainants. Michigan and New York filed separately in 1926.

Their claim: the diversion had lowered the levels of Lakes Michigan, Huron, Erie, and Ontario, their connecting waterways, and the St. Lawrence above tidewater by not less than 6 inches.

Six inches across 4 lakes is a staggering volume of water, and it hit harbors, shipping, and shoreline property across 6 states.

Downstream states along the Mississippi (Missouri, Kentucky, Tennessee, Louisiana, Mississippi, and Arkansas) intervened on Illinois’s side. They liked the extra flow.

Was the Chicago diversion authorized, and could the Secretary of War permit a diversion of Great Lakes water for sewage disposal at the expense of lake levels and navigation?

Holding and reasoning

The Court held the diversion was far in excess of what navigation needed, and that the excess was unlawful.

The permitting authority did not stretch that far. The Secretary of War’s power under the Act of March 3, 1899, ran to navigation. It was not a license to authorize diversions whose real purpose was carrying away Chicago’s sewage.

The Court acknowledged that Chicago had a genuine sanitation problem and could not simply be ordered to stop overnight. Its remedy was structural: Illinois had to build sewage treatment capacity so it would no longer need dilution water, and step the diversion down on a schedule.

The follow-on decreedecreeThe court order at the end of an adjudication, spelling out exactly who gets how much water and in what order. of April 21, 1930 (281 U.S. 696) set the terms. Starting July 1, 1930, diversion was capped at an annual average of 6,500 cubic feet per secondcubic feet per secondA flow rate rather than a volume. 1 cubic foot per second running all day is about 2 acre-feet. plus domestic pumpage, stepping down over time to 1,500 cubic feet per second plus domestic pumpage. The Sanitary District had to file semi-annual progress reports with the Court on its treatment plant construction.

Congress ratified the arrangement in the Act of July 3, 1930.

Why it matters

The Great Lakes hold roughly 20 percent of the world’s surface fresh water, and this case is where the region learned that a single city could measurably lower all of them.

It set the emotional and legal baseline for Great Lakes politics. Diversion is treated as presumptively illegitimate here, and the burden falls on whoever wants to take water out.

The Court never let go. The Chicago diversion has been under a continuing Supreme Court decreedecreeThe court order at the end of an adjudication, spelling out exactly who gets how much water and in what order. for roughly a century, modified repeatedly, with Illinois accountable for its accounting. There is no other American water arrangement quite like it.

The unresolved anxiety in the case is also the modern one. Water taken from the Great Lakes basin and sent to the Mississippi system doesn’t come back. Consumptive loss from a closed basin is permanent in any practical sense.

That anxiety produced the Great Lakes Charter in 1985, its 2001 Annex, and finally the Great Lakes-St. Lawrence River Basin Water Resources CompactcompactA binding agreement between states that Congress approves. Once approved it becomes federal law and overrides conflicting state rules. The Great Lakes Compact is one., which Congress consented to in Public Law 110-342 on October 3, 2008. The CompactcompactA binding agreement between states that Congress approves. Once approved it becomes federal law and overrides conflicting state rules. The Great Lakes Compact is one. bans new or increased diversions outside the basin, with narrow exceptions for straddling communitiesstraddling communityA town sitting partly inside and partly outside the Great Lakes basin. It can apply to divert water with its own state's approval. and straddling counties.

What it means for a landowner today

Nothing here governs a specific parcel, and everything here shapes the regime around it.

Practical translation for a Wisconsin buyer near Lake Michigan:

  • Great Lakes water is the most legally protected fresh water in the country. That’s a genuine long-term positive for the region.
  • Protection cuts both ways. The same regime that blocks Arizona-style exports also constrains local withdrawals, especially high capacity wellshigh capacity wellIn Wisconsin, a well (or all wells on 1 property combined) capable of pumping 100,000 gallons a day or more. These need DNR approval. An ordinary house well does not. that draw from groundwater connected to surface water.
  • Your parcel’s position matters. Inside the Great Lakes basin, straddling the divide, or outside it entirely changes which rules apply to a large water user, and Wisconsin has communities in all 3 positions.

What to verify: whether the parcel sits inside the Great Lakes basin boundary, which municipal water system serves it and where that system draws from, and whether any planned well would need a high capacity wellhigh capacity wellIn Wisconsin, a well (or all wells on 1 property combined) capable of pumping 100,000 gallons a day or more. These need DNR approval. An ordinary house well does not. approval. Who verifies: the Wisconsin DNR and a hydrogeologisthydrogeologistA geologist who specializes in groundwater. Worth hiring for acreage, tricky geology, or any large planned withdrawal..

The Waukesha diversion approval in 2016, the first for a community in a straddling countycommunity in a straddling countyA town entirely outside the Great Lakes basin but inside a county the basin line crosses. It needs all 8 Great Lakes governors to agree. Waukesha is the only one that has ever succeeded., is the live example of how narrow the exceptions are. See ../03-wisconsin-great-lakes/.

Subsequent history / is it still good law

Good law as of July 2026, and unusually alive for a 1929 case. The decree has been modified several times, most substantially in 1967 and 1980, and the case remains on the Supreme Court’s original docket.

The current framework caps the Illinois diversion at a long-term annual average of 3,200 cubic feet per second, measured over a 40-year running average. [UNVERIFIED] as to the precise current averaging terms; confirm against the operative decree and the Army Corps annual accounting before relying on the number.

Michigan has returned to the Court more than once seeking modifications. The 2008 Compact now governs new diversions, while the Chicago diversion continues under the Court’s separate decree because it predates and sits outside the Compact.

Sources

Research demo, not legal advice. Facts current as of July 2026. Water law is state-specific and moves quickly, so confirm anything you plan to act on with a licensed attorney and the relevant state agency.