Point source versus nonpoint source pollution
The Environmental Protection Agency’s (EPA) CWA website defines point source pollution as: pipes or man made ditches that discharge pollutants into US waters. This includes discharges from municipal sewage plants and industrial facilities, but also collected storm drainage from larger urban areas, certain animal feedlots and fish farms, some types of ships, tank trucks, offshore oil platforms, and collected runoff from many construction sites.
Nonpoint source pollution is any pollution that isn't a point source. It reaches surface waters as a direct result of rainfall or snowmelt moving over and through the ground and is sometimes referred to as “poison runoff." When it rains, water accumulates on man-made surfaces such as roads, roofs and parking lots -- hard surfaces that prevent water from soaking into the ground. Runoff from the land that flows into other bodies of water -streams, rivers and lakes - carries many contaminants including sediment, phosphorus, nitrogen, toxic metals, herbicides and pesticides, organic material, oil compounds, and bacteria. Roadways release oil and grease, tailpipe emissions, and other toxics from motor vehicles. Lawns allow drain-off of fertilizers and animal waste. Construction sites release quantities of mud which contribute to erosion. Commerical and industrial areas can be a source of heavy metals.
In addition to polluting the water, runoff creates havoc when it floods streams or lakes. The increased water flow erodes stream banks, destabilizes stream contours and changes depths. Accumulated runoff eventually finds its way into large bodies of water like the Great Lakes, Mississippi River, Chesapeake Bay, Long Island Sound, Puget Sound and the Gulf of Mexico and causes even greater problems.