Stormwater discharges are generated by precipitation and runoff from land, pavements, building rooftops and other surfaces. Stormwater runoff can accumulate pollutants such as oil and grease, chemicals, nutrients, metals, and bacteria as it travels across land. Heavy precipitation or snowmelt can also cause sanitary sewer overflows which, in turn, may lead to contamination of water sources with untreated human and industrial waste, toxic materials, and other debris. Water pollution from runoff degrades surface waters and can make them unsafe for drinking, fishing, swimming, and other activities, as well as degrading wildlife habitat.