In case you hadn't noticed, the Chicago River flows backwards. It's been doing this for over a hundred years.
Like any normal river, the Chicago River used to flow into a larger body of water--namely, Lake Michigan. This became a problem in the middle of the 19th Century. As Chicago grew into a major city, the raw sewage of civilization was dumped into the river and flushed through to the lake. And the lake was where Chicagoans got their drinking water.
Besides being gross, this was dangerous. All those germs in the drinking water produced outbreaks of cholera or typhoid or other diseases.
You'll often hear the story of the Great Chicago Plague. It's said that cholera wiped out 70,000 people in a single year, about 20% of the city's population. Don't believe it. Someone cooked up the tale to make a point.
In any case, the solution to the pollution was simple. Just reverse the flow of the river so that it didn't empty into the lake.
Build a barrier at the east end of the Chicago River to block it off from the lake. At the same time, connect the west end to the Des Plaines River. Then our water would flow through the Des Plaines into the Illinois River, which flowed into the Mississippi River, which carried everything off into the Gulf of Mexico, a thousand miles away.
At first the engineers tried to deepen the Illinois & Michigan Canal, and use it as the west-end drain. That didn't work. A new canal was needed, and in 1889 the Illinois legislature approved plans to build the Chicago Drainage Canal.
Digging began in 1893. The Drainage Canal was going to be 28 miles long, 24 feet deep, and 202 feet wide. It was said to be the greatest public works project in history.
As the canal neared completion, some downriver towns weren't happy about Chicago sewage flavoring their drinking water. St. Louis prepared a lawsuit to halt the project.
Politicians love to hold dedication ceremonies, to show voters that tax dollars are being wisely spent. Now they couldn't wait. On the morning of January 2, 1900, an anonymous flunky simply opened the sluice gate, and the Chicago River began flowing into the new canal. Fait accompli!
Today the drainage canal is called the Chicago Sanitary and Ship Canal. Meanwhile, two other waterways have been built to aid its noble work.
And if you look at the census figures, you'll note that the population of St. Louis keeps getting smaller and smaller. Is it something in their water?