The Chicago River is a system of rivers and canals that runs through the city of Chicago, including the City Center.

The river is also noteworthy for its natural and human-engineered history. In 1887, the Illinois General Assembly decided to reverse the flow of the Chicago River through civil engineering by taking water from Lake Michigan and discharging it into the Mississippi River watershed, partly in response to concerns created by an extreme weather event in 1885 that threatened the city's water supply. In 1889, the state created the Chicago Sanitary District to replace the Illinois and Michigan Canal with the Chicago Sanitary and Ship Canal, a much larger waterway, because the former had become inadequate to serve the city's increasing sewage and commercial navigation needs. Completed by 1900, the project reversed the flow of the main stem and South Branch and altered the flow of the North Branch by using a series of canal locks and pumping stations, increasing the flow from Lake Michigan into the river, causing the river to empty into the new canal instead.