Nonpoint source pollution (NPS pollution) is the diffuse contamination of water bodies that originates from widespread, scattered sources rather than a single, identifiable discharge point. In stormwater management and watershed science, it refers to pollutants that are transported by precipitation, snowmelt, or irrigation water as it moves over and through the landscape, eventually reaching surface waters or groundwater.
Unlike point source pollution, which enters receiving waters through a discrete conveyance such as a pipe or outfall, nonpoint source pollution is generated across broad areas, making it more difficult to identify, regulate, and control. Common sources include urban runoff from streets and parking lots, agricultural runoff from fields and livestock areas, construction site erosion, forestry activities, and residential landscapes.
As water moves across the land as overland flow, it can pick up and transport a wide range of pollutants. These include sediment, nutrients such as nitrogen and phosphorus, pesticides and herbicides, heavy metals, oils and grease, pathogens, and debris. The type and concentration of pollutants depend on land use, surface conditions, and human activities within the watershed.
Nonpoint source pollution is a leading cause of water quality impairment in many regions. It can increase turbidity, degrade aquatic habitats, contaminate drinking water supplies, and contribute to problems such as eutrophication in lakes, ponds, and estuaries.
Because it is diffuse in nature, management of nonpoint source pollution relies on the implementation of best management practices (BMPs) that reduce pollutant generation and transport. These practices include erosion and sediment controls, vegetative buffers, infiltration systems, proper nutrient management, and public education.
Nonpoint source pollution represents a critical challenge in stormwater management, requiring comprehensive, watershed-based approaches to effectively reduce its impacts and protect receiving waters.