I'd Like to Go Swimming in That Volcano
True or false: it is possible for a lake to exist at the top of a mountain with no streams running into or out of it.
True. Crater Lake sits on the top of a mountain and has no streams running into or out of it. How? Mount Mazama, on top of which Crater Lake sits, used to be an active volcano. About 7,700 years ago it erupted violently, and then collapsed in on itself. That created a caldera - a big bowl shaped hole - at the top of the mountain. After a few hundred years of rain and snow, the hole filled up, and Crater Lake was born. The lake endures because the amount of water that evaporates and seeps into the mountain each year is usually very close to the amount of rain and snowfall.
Crater Lake is the deepest lake United States and is incredibly clear because nothing ever gets into the lake except water. No streams means no fish, no dirt, no sediment, nothing.