In this episode of Crash Course Kids, Sabrina talks about a few different examples how some freshwater sources were good, then bad, then made good again. Also, Sabrina talks about parasites, fish, and dams! [4:10]

We have a lot of water on Earth, but we also can't actually drink much of it or use it for farming. That's because most of the water on Earth is saltwater. We humans, like a lot of living things, need freshwater to survive. In this...