Stormwater, as defined by Clean Water Act regulations, is “stormwater runoff, snowmelt runoff, and surface runoff and drainage,” or precipitation that runs off streets, lawns and other land surfaces.
Stormwater runoff is considered a nonpoint source pollutant because it comes from many diffuse sources. Population growth resulting in rapid development is a primary threat to watersheds with an increase in impervious surfaces such as building roofs, sidewalks, and parking lots. Instead of stormwater slowly and naturally soaking into the ground and eventually filling streams and lakes, impenetrable surfaces cause water to rush too quickly back into the water bodies.