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Table 1--Common causes of pollution summarized from National Water Quality Inventory Reports

Cause of impairment	Description of cause
Nutrients	Nitrates found in sewage and fertilizers and phosphates found in detergents and fertilizers.
Siltation (sedimentation)	Wash off plowed fields, construction and logging sites, urban areas, strip-mined land, and eroded stream banks.
Pathogens (bacteria)	Inadequately treated sewage, storm water drains, septic systems, runoff from livestock pens, and boats that dump sewage.
Organic material	Sewage, leaves and grass clippings, and runoff from livestock feedlots and pastures.
Metals	Industrial discharges, runoff from city streets, mining activities, and leachate from landfills.
Pesticides and herbicides	Runoff from croplands, lawns, and termite control.
Habitat modification	Grazing, farming, channelization, dam construction, and dredging.

Source: U.S. Environmental Protection Agency 1994

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