Stormwater runoff is water from rain or melting snow. It flows from rooftops, over paved streets, sidewalks, across bare soil, and through lawns and storm drains. Polluted runoff from farms, construction sites, homes and public spaces is now widely recognized as the single largest threat to water quality in the United States.
When it rains, water flows across impervious surfaces, collecting pollutants like pet waste, salt, pesticides, fertilizer, oil, grease, litter, and soil along the way. Increased volumes of rainwater, or runoff, flows untreated through a system of storm sewers into area rivers, lakes, and streams. Polluted stormwater can kill or damage plants, fish and wildlife, while degrading water quality in local watersheds.