Why did the Chicago River flow reversal divert water from Lake Michigan?

The Chicago River’s flow was reversed primarily to protect public health by preventing the contamination of Lake Michigan. Originally, the river emptied into the lake, which served as the city's primary source of drinking water. Following a severe storm in 1885 that caused the river to discharge large amounts of sewage-polluted water into the lake, officials initiated the construction of the Chicago Sanitary and Ship Canal.12

Completed in 1900, this engineering project successfully reversed the river's flow, directing it inland away from the lake. The water now flows through the canal system into the Des Plaines River and eventually toward the Mississippi River watershed. This monumental effort was essential to halt the pollution of the city's water supply and remains a significant example of large-scale civil engineering.132