What is a watershed?
“Watershed” has several meanings, including a specific technical meaning in the field of hydrology. For our purposes here, a watershed is an area of land that drains into a river, river system, or other body of water. A watershed captures precipitation, filters and stores water, and influences where and how water moves. A watershed can be large or small, and smaller watersheds join together in a network to become larger watersheds. Any activity that affects water quality, quantity, or movement at one location can change the characteristics of the watershed at locations downstream. (USDA USFS Wild Waters)
U.S. Environmental Protection Agency
Article - What is a Watershed?
Conservation Technology Information Center
Article - What's a Watershed?
U.S. Geoogical Survey: "The Water Cycle"