Why does the Chicago River flow backwards?

The Chicago River sometimes flows backwards because people built something special to help it do that.

Imagine you're playing with water in your bathtub. You can turn on the faucet and let water flow out, or you can use a little pump to send water back in, like magic, but not really magic. That’s what people did with the Chicago River. They built pumps that push water from one part of the river to another.

Normally, water flows from high places to low places, just like when you pour juice from a tall glass into a short one. But sometimes, the pumps work so hard that they send water backwards, from lower parts of the river to higher ones. It’s like giving the river a little push, or even a big shove!

This is why, on some days, you can see water flowing in the opposite direction, and it looks like the river is playing a fun game with itself.