Chicago River’s Flow Reversed Over a Century Ago for Sanitation
In 1900, Chicago engineers reversed the flow of the Chicago River to divert the city's sewage away from Lake Michigan and towards the Mississippi River. St. Louis's legal challenge to stop this at the Supreme Court was unsuccessful, and the…
St. Louis, MO, September 12, 2026 — The Chicago River’s flow was intentionally reversed in 1900 as a significant public works project aimed at improving sanitation and protecting the city’s drinking water supply. This monumental engineering feat diverted the river’s natural course away from Lake Michigan, the source of Chicago’s freshwater, and instead directed its waters, including sewage, towards the Des Plaines River, which then flows into the Illinois River and eventually the Mississippi River.
This decision followed extensive planning and execution by Chicago engineers. The primary objective was to move the city’s wastewater downstream, away from the lake that supplied its drinking water. Prior to this reversal, untreated sewage was discharged directly into Lake Michigan, leading to significant public health concerns and contamination.
The reversal of the river’s flow was not without its legal challenges. The city of St. Louis, located downstream, filed a lawsuit seeking to halt the project. St. Louis argued that the diversion would negatively impact its own water supply and environment. However, the case was brought before the Supreme Court, which ultimately ruled against St. Louis, allowing the altered flow of the Chicago River to continue.
Over a century later, the Chicago River’s flow remains reversed, a testament to the enduring impact of this 1900 decision. The project is often cited as a remarkable example of urban engineering designed to address critical public health and environmental issues of its time. While the reversal solved immediate sanitation problems for Chicago, the long-term downstream environmental consequences have been a subject of ongoing discussion and management by authorities along the connected waterways. The name of the specific Supreme Court case, the precise arguments presented by both cities, and further details on the engineering specifics beyond the primary objective were not provided in the summary. The contractor’s name and the exact duration of construction are also not detailed in the available information.
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