Stormwater runoff from streets, lawns, parking lots, construction sites, industrial facilities, and other impervious surfaces occurs as a result of precipitation events (for example, rain water or melted snow). The stormwater runoff may enter surface waters directly or through natural and constructed channel systems.
Activities occurring in developed and urban areas contaminate stormwater runoff with pollutants such as automobile oil, grease, metals, sediment, nutrients and pesticides, as well as deposits from airborne pollutants.
Unmanaged stormwater can cause erosion and flooding. It also can carry excess nutrients, sediment and other contaminants into rivers and streams. Properly managed stormwater can recharge groundwater and protect land and streams from erosion, flooding and pollutants.