Why Watersheds?

A watershed is the land area that drains to a common body of water, such as a stream, lake, estuary, wetland, or even the ocean.

Everyone lives in a watershed! Watersheds provide our drinking water, habitat for wildlife, soil in which to grow our food, and the streams, rivers and lakes we use for fishing, boating and swimming. We all share a common interest in having a healthy watershed. To learn more about YOUR watershed, visit EPA's Surf Your Watershed.

The EPA has long promoted using a watershed approach to manage our land and water resources. The scientific basis for this approach is documented by research on the important connection between land use and watershed health.

During the land development process, forests are cleared, soils are compacted, natural drainage patterns are altered, and impervious surfaces such as roads, buildings and parking lots, are created. These changes increase the amount of polluted runoff that reaches our local waterways. As a result, stream banks begin to erode, critical in-stream habitats are washed way or filled in with sediment, downstream flooding increases, and water becomes too polluted to support sensitive fish and bugs or recreational activities. For more information on the impacts of urbanization on watershed health, see:

  • The Impacts of Impervious Cover on Aquatic Systems. This Center for Watershed Protection report compiles more than 225 multi-disciplinary studies documenting the hydrological, physical, water quality, and biological impacts of urbanization and its accompanying impervious cover. This manual is available for purchase at our Store (hard copy) and the electronic version can be downloaded for free on our Free Downloads page.
  • Effects of Urbanization on Stream Ecosystems. The U.S. Geological Survey's National Water-Quality Assessment Program study on the effects of urbanization on stream ecosystems examines the magnitude and pattern of response in stream biological communities, hydrology, habitat, and water chemistry as watersheds are urbanized in 10 metropolitan areas across the US.
  • Silent Streams. The Washington Post Magazine's cover story, from November 2005, describes how sprawl is threatening almost every stream in the country and reviews many Center principles regarding the impact of impervious cover on water resources.