Which U.S. River Is Famous For Flowing Backward?
The river widely known for flowing backward is the Chicago River in Illinois, because engineers actually reversed its natural direction in the early 1900s.
Instead of letting polluted water flow into Lake Michigan, the city turned the river around so it now drains toward the Des Plaines, Illinois, and eventually the Mississippi River system.
It sounds like a myth, but this “backward river” is still doing its job today and is often mentioned in geography quizzes and travel trivia as the classic example of a U.S. river that was made to run the other way.
Where Is The Chicago River Located?
The Chicago River flows through the city of Chicago in the state of Illinois, in the American Midwest, connecting to Lake Michigan at its eastern end.
It winds through downtown, under low bridges and past high‑rise buildings, and then links via canals to the Des Plaines and Illinois rivers to the west.
For many visitors, that green‑dyed river on St. Patrick’s Day in the middle of Chicago is their first visual proof that this is the same waterway with the “backward” story attached to it.
Why Was The Chicago River’s Flow Reversed?
The flow was reversed mainly to protect Chicago’s drinking water in Lake Michigan from sewage and industrial waste that used to be dumped into the river.
By the late 1800s, fast population growth meant that every heavy rain pushed contaminated river water back into the lake, leading to serious outbreaks of waterborne disease.
City and state leaders decided that instead of letting sewage head straight toward the intake cribs in the lake, they would send it away from the lake and into the Mississippi River watershed, which felt like choosing the “less bad” option at that time.
How Was The Chicago River Made To Run Backward?
Engineers reversed the Chicago River by digging the Chicago Sanitary and Ship Canal, a 28‑mile channel that lowered the river’s outlet and pulled water away from Lake Michigan.
Completed around January 2, 1900, the canal, combined with locks, dredging, and pumping, changed the water level enough that the main stem and South Branch started flowing west instead of into the lake.
It was a massive job: tens of millions of cubic yards of soil and rock were removed, and the project was later honored as a “Civil Engineering Monument of the Millennium” for how dramatically it reshaped both the city and the region’s waterways.
A few simple takeaways that make this feel less abstract:
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The canal connects Chicago to the Des Plaines River, then the Illinois, then the Mississippi.
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In big storms, modern operators sometimes temporarily “re‑reverse” flow toward the lake to control flooding, which shows the system is still actively managed, not just a relic of the past.
When Did The Chicago River Start Flowing Backward?
The Chicago River officially began flowing backward in early January 1900, when the gates of the new sanitary canal at Lockport were opened.
Planning started years earlier, with the Illinois General Assembly authorizing the reversal in the late 1880s and the Sanitary District of Chicago formed in 1889 to carry it out, but 1900 is the date usually given as the moment the river’s direction truly changed.
In 2025, Chicago even marked the 125th anniversary of the reversal, treating it as a turning point in the city’s public‑health history and as a reminder that water infrastructure decisions still affect communities far downstream today.
Disclaimer: Information about the Chicago River, its location, and the engineering work that reversed its flow is provided for general educational and informational purposes only and may not reflect the latest technical, legal, or environmental updates. Readers should refer to official city, environmental, or engineering sources for precise data or for decisions related to travel, research, or infrastructure planning.
