Chicago River Reversal: The City That Made Its River Run Backward, Illinois

In the 1800s, Chicago had a deadly arrangement. The city's sewers drained into the Chicago River, and the Chicago River drained into Lake Michigan, the city's source of drinking water. In heavy rains, sewage pushed out into the lake and toward the water intakes offshore. Typhoid, cholera and dysentery followed. The city tried a fix once already. In 1871, the old Illinois and Michigan Canal was deepened so the river would flow away from the lake, but the reversal lasted only one season. In 1889, the state of Illinois created a new agency, the Sanitary District of Chicago, to solve the problem for good. Its plan was enormous. Chicago sits on a low ridge that divides two watersheds. On one side, water flows to Lake Michigan and the Atlantic; on the other, to the Des Plaines and Illinois rivers and down the Mississippi to the Gulf of Mexico. If engineers cut a deep enough canal through that ridge, the Chicago River would flow away from the lake, carrying the city's wastewater with it. Work on the Chicago Sanitary and Ship Canal began in 1892. Crews dug a 28-mile channel from the Chicago River to Lockport, removing about 42 million cubic yards of soil and rock. The final 15 miles were cut through bedrock with dynamite and steam shovels mounted on rails. The canal was designed to get deeper as it ran west, so water would flow toward Lockport. Not everyone downstream wanted Chicago's sewage. Missouri was preparing to go to court to stop the canal from opening. So on January 2, 1900, Chicago officials quietly removed the last dam between the river and the canal before a judge could act. Water began pouring west, and by January 17, the full flow had been released. Missouri sued anyway. The case reached the U.S. Supreme Court, which eventually ruled in Chicago's favor. The Chicago River now flowed out of Lake Michigan instead of into it, and the city's drinking water became safer. In 1955, the American Society of Civil Engineers named the reversal one of the seven wonders of American engineering, and in 1999 it called the Chicago River system a "Monument of the Millennium." But the river doesn't always obey. Later legal fights over how much water Chicago could take from the lake led the Sanitary District, now the Metropolitan Water Reclamation District, to build the Chicago Harbor Lock between 1936 and 1938 to control the flow. Its gates normally let lake water into the river. In extreme storms, when the river rises higher than the lake, the district opens them the other way, as a last resort, and lets the river pour back into Lake Michigan. That happened most recently on July 2, 2023, when parts of the city got eight inches of rain. For more than 125 years, the Chicago River has flowed backward from its natural course, nearly all the time.