What's a watershed?
A watershed is the area of land that catches rain or snow, which in turn drains into a river or stream system. As rain falls, or snow and ice melts, the water follows gravity and flows into streams, rivers, and other bodies of water, such as a marshes or lakes.
Watersheds come in all shapes and sizes. They cross county, state, and national boundaries, and can be subdivided into smaller and smaller units. There are more than 50 watersheds in Pennsylvania.