Water Pollution

Point-source pollution enters water bodies at identifiable locations—factory outfall pipes, sewage treatment plant discharges, or oil spills. The U.S. Clean Water Act regulates point sources through National Pollutant Discharge Elimination System (NPDES) permits that set effluent limits. Nonpoint-source pollution comes from diffuse areas: agricultural runoff carrying fertilizers and pesticides, urban stormwater washing oil and heavy metals from roads, and atmospheric deposition of mercury. Nonpoint sources are far harder to regulate and now account for the majority of water quality impairments in U.S. rivers and streams. Both types can devastate aquatic life and compromise drinking water supplies.