Reversing the Chicago River solved one crisis and created another

Kolbert opens with the engineering feat of reversing the flow of the Chicago River in the early twentieth century, a project undertaken to stop sewage from contaminating the city's drinking water supply in Lake Michigan by redirecting waste toward the Mississippi River basin instead. The project succeeded at its original goal, but it also created an artificial water connection between the Great Lakes and Mississippi watersheds that had never existed naturally, eventually opening a corridor for invasive species, most notoriously Asian carp, to threaten to move between the two systems. Decades later, engineers built electric barriers in canals specifically to stop carp from completing that migration, an expensive, ongoing intervention required only because of the earlier fix. Kolbert treats this as the book's founding parable: solving one problem through engineering routinely generates a new problem requiring its own engineered solution. Takeaway: even wildly successful interventions can quietly seed the next generation's environmental crisis.