Chicago reversed its river in 1900 to divert sewage from Lake Michigan; 126 years later, it flows backwards

Chicago's founding problem had always been plumbing. The city drew its drinking water from Lake Michigan and emptied sewers into the Chicago River, which flowed straight into Lake Michigan. But every rainstorm flushed the stockyards and slaughterhouses and a million people's waste out toward the water intakes. This is why the nineteenth-century city was periodically ravaged by typhoid, cholera, dysentery and more. This is when the city came up with a solution: if the river ends in the wrong place, turn it around.Creating a ditchRivers don't turn around on command. But Chicago is near a low ridge. That ridge separates the Great Lakes basin from the Mississippi River basin. Engineers had a simple idea. Dig a deep ditch towards the Des Plaines River, and gravity would take the water the other way.The tool created to do this was the Chicago Sanitary and Ship Canal, a 28-mile channel cut from the river's South Branch to Lockport, crossing the low subcontinental divide that separates the Great Lakes basin from the Mississippi’s. Dig deep enough, and gravity itself could be re-hired: lake water would pour into the Chicago River, push its whole flow backwards, and carry the city’s diluted ...