In the late 19th century, Chicago faced a severe public health crisis. The Chicago River carried urban sewage and industrial waste directly into Lake Michigan, which served as the city's primary source of fresh drinking water. Deadly outbreaks of cholera and typhoid fever repeatedly devastated the population.
To permanently solve the crisis, the Sanitary District of Chicago undertook one of the greatest civil engineering projects in human history: reversing the flow of the Chicago River. Led by chief engineer Isham Randolph, workers excavated the 28-mile Chicago Sanitary and Ship Canal between 1892 and 1900. By cutting through the Subcontinental Divide near Lockport, Illinois, engineers created a gradient lower than the level of Lake Michigan.
When the canal sluice gates opened in 1900, gravity took over, causing the Chicago River to flow backward, away from the lake and toward the Des Plaines and Mississippi River basins. Central to managing this massive artificial hydrology is the Lockport Controlling Works. This complex of dams, sluice gates, and locks controls the discharge rate of Chicago's river system, managing water levels to prevent flooding while ensuring adequate sanitation flow and navigable depths for commercial barge traffic.
The project drastically improved public health, though it sparked legal battles from downstream cities and forever altered Midwest watersheds.