A watershed is an area of land that drains water, such as rain, runoff or wastewater, into a common outlet, such as a drain, stream or river. These common outlets function to provide drinking water; recreational opportunities, such as fishing and swimming; water for use in industry and agriculture; and plant and animal habitats.
Colloquially, the term "watershed" is often applied to an area immediately surrounding a river, stream or gully that a watershed drains into or to the outlet itself. In many cities, watersheds are associated with greenways and parks, which are often developed along areas where a watershed drains into a stream or river flowing through the city.
Watershed protection or management refers to protecting the area that drains into an outlet, such as a river or stream, from pollutants to protect the outlet as well as its associated habitats. Some common sources of watershed pollutants include chemicals used in agriculture, farm animal waste and overflowing sewers, as well as activities such as dumping used motor oil on the ground or washing one's car with harmful chemicals. In addition to human activities, the growth of some algae and exotic or invasive species in watersheds contributes to the pollution of streams and rivers.