At the end of the 19th century, Chicago had a problem that was killing its citizens: the city was dumping its raw sewage into the Chicago River, which flowed straight into Lake Michigan — the same lake that supplied its drinking water. Typhoid and cholera outbreaks were rampant, and moving the water intake further offshore only bought temporary relief.

The solution was audacious: rather than clean up the sewage, engineers decided to reverse the flow of the river itself. By digging the Chicago Sanitary and Ship Canal — a 28-mile channel cut through solid rock and clay — they lowered the river's downstream elevation enough that gravity pulled it backwards, away from Lake Michigan and toward the Mississippi River basin instead.

The project was so large it drove innovations in earth-moving equipment that were later used on the Panama Canal, and it was named one of the Seven Wonders of American Engineering. It's also a fascinating case study in externalizing a pollution problem — St. Louis, downstream, was famously not amused and sued to stop it.

The Daat's short-form treatment packs the geography, the political drama, and the engineering ingenuity into a tight explainer. A great pick for anyone interested in civil engineering, public health history, or the surprisingly aggressive things cities have done to fix infrastructure problems.