On a rainy day look out the window and see if you can determine where the water goes during a rain shower. A watershed is a region in which all water drains off the land into small rivers and streams, which in turn, drain into one main river. For example, the Mississippi River watershed covers most of the Midwest and some the West, including the Rockies. All water within that region eventually drains into the Mississippi River. A watershed is made up of not only a large river, but also its tributaries.
Tributaries are the smaller rivers and streams that flow into the larger river.
The large river eventually reaches the ocean, carrying along the way excess water drained from land by its watershed. Water not absorbed by roots enters the ground water supply by infiltration. Most water runs off the surface, down a hill and eventually into a river. Ditches and small streams, which may be dry when it does not rain, can quickly fill up with water when it does rains. If you have ever studied a map in detail, you will notice how rivers and streams form a network of waterways across the countryside.