What Is A Watershed?
No matter where you live, work, or play, you're in a watershed! So what is a watershed, and how does it work? A watershed is an area of land where all the water (surface and groundwater) flows to the lowest point—usually a stream, lake, or river.
Imagine your bathtub is a watershed and the drain is a river. Any water that falls inside the tub (watershed) will eventually go down the drain (river) carrying dirt and soap with it. The high sides of the tub (like mountains and hills) keep the water from ending up on the floor (or in other watersheds).
Each small watershed is part of the more extensive watershed for a larger stream or lake in the vicinity. These larger watersheds are, in turn, part of even larger drainage networks and so on. The largest-scale watershed is called a basin. Pennsylvania has six basins, some of which include portions of neighboring states.