Watersheds are regions that are drained by a single river or stream. Think of a bathtub after the shower has run. All the water runs off the walls and the sides of the tub toward the bottom of the tub. From there, it runs down the drain. That's a little like what a watershed is like. In the forest, watersheds are areas between high ridges.

Water in the Boise River comes from springs and streams in the Boise National Forest. Little streams flow into bigger streams. They flow into even bigger streams. Eventually, the streams flow into the river!