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Can a River Flow Backwards?

Rivers flowing backwards may sound like a natural anomaly, but it's a phenomenon that can occur under certain conditions, such as geological shifts or powerful weather events. Understanding the forces that can reverse a river's flow reveals much about our planet's dynamic systems. How does this happen? Let's examine the intriguing science behind this rare event. What might cause a river near you to defy expectations?

It's dyed green for St. Patrick's Day, but that's not the weirdest thing about the Chicago River. The 156-mile (251-km) stretch of water is the only river in the world to permanently flow backward. This wasn't a natural occurrence, though. It came about in the late 19th century, when city officials decided that the best way to prevent the ongoing influx of pollution from entering Chicago's water supply was to reverse the river's course, sending all of the nastiness back into the mighty Mississippi.

Engineers built a 28-mile-long (45-km) canal that became deeper as it went west, thus pulling water from Lake Michigan and sending it away in the opposite direction. It took eight years for the project to be completed. Decades later, the American Society of Civil Engineers named it one of the world's seven wonders of engineering.

That toddlin' town:

  • In 1942, the atom was split for the first time at the University of Chicago.

  • It is possible to see Indiana, Michigan, and Wisconsin – as well as Illinois, of course – from the top of Chicago's Willis Tower.

  • Twinkies, brownies, and the Ferris wheel all got their start in Chicago.

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    • In 1900, the flow of the Chicago River was reversed, away from Lake Michigan and towards the Mississippi River watershed.
      In 1900, the flow of the Chicago River was reversed, away from Lake Michigan and towards the Mississippi River watershed.