Non-point source pollution is pollution which enters a watershed through runoff from precipitation.  As the runoff moves, it picks up and carries away natural and human-made pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters, and even our underground sources of drinking water.

Some examples of nonpoint source pollution are:

• Excess fertilizers, herbicides, and insecticides from agricultural lands and residential areas;
• Oil, grease, and toxic chemicals from urban runoff and energy production;
• Sediment from improperly managed construction sites, crop and forest lands, and eroding streambanks;
• Salt from irrigation practices and acid drainage from abandoned mines;
• Bacteria and nutrients from livestock, pet wastes, and faulty septic systems;

Atmospheric deposition and hydromodification are also sources of nonpoint source pollution.

From the EPA's Non-Point Source Pollution Information Page