It occurs when substances such as human and other animal wastes contaminate water, toxic chemicals, metal and oils.
Pollution can affect rain, rivers, lakes, oceans and groundwater.
Both natural processes and human activity can cause water pollution. Both surface water and groundwater can be polluted with minerals leached from the soil, acids from decaying animal products. Pollutants can come from agricultural, urban and industrial sources, as well from untreated human wastes. Polluted water may look clean, but it contains germs, chemicals or other materials that can be harmful and cause illness or even death. Industrial wasters is the primary cause of water pollution in the United States.