In the late 19th century, Chicago was growing at a breakneck pace, but it faced a deadly, self-made crisis: its drinking water was poisoned. The Chicago River served as an open sewer for meatpacking plants, factories, and hundreds of thousands of residents, emptying directly into Lake Michigan—which happened to be the city's primary source of freshwater. Heavy rainstorms routinely washed massive plumes of filth far out into the lake, triggering catastrophic outbreaks of cholera and typhoid fever.
Desperate for a solution, city leaders approved an audacious plan engineered by the Sanitary District of Chicago. Instead of cleaning up the waste, they decided to bend nature to their will. Engineers planned to dig a massive, 28-mile artificial waterway—the Chicago Sanitary and Ship Canal—that would connect the Chicago River to the Des Plaines River.
Because the Des Plaines sat at a lower elevation across the sub-continental divide, opening the canal would pull water from Lake Michigan, into the Chicago River, and push the city's effluent south toward the Mississippi River basin instead. Between 1892 and 1900, crews excavated over 42 million cubic yards of earth and rock, utilizing revolutionary earth-moving equipment that would later be deployed on the Panama Canal. Fearing that the neighboring state of Missouri would obtain a federal injunction to block the river's pollution from flowing toward St.
Louis, Chicago officials acted in secret. Before sunrise on January 2, 1900, workers secretly chopped through the final rock dam, permanently forcing the Chicago River to flow backward. When Missouri finally filed its lawsuit days later, it was too late—the river was already running south.
The operation successfully spared Chicago from deadly waterborne epidemics, making it the only major river in the world forced to run entirely away from its natural mouth.