Nonpoint source (NPS) pollution occurs when rain runs off farmland, city streets, construction sites, suburban lawns, roofs and driveways, and enters our waterways. The runoff often contains harmful substances, such as toxics, pathogens, excess nutrients and sediments. It is called nonpoint source pollution because it does not come from a single source, or point, such as a sewage treatment plant or an industrial discharge pipe. Therefore, nonpoint source pollution does not meet the legal definition of "point source" in the Clean Water Act.

There are four main forms of nonpoint source pollution: sediments, nutrients, toxic substances and pathogens.

• Sediments are soil particles carried by rainwater into streams, lakes, rivers and bays. By volume, sediment is the greatest pollutant of all. It is caused mainly by erosion resulting from bare land, some farming practices, and construction and development.
• Nutrients are substances that help plants and animals live and grow. The main concern is excessive amounts of two nutrients: nitrogen and phosphorus. 
• Toxic substances are chemicals that may cause human and wildlife health concerns. They include organic and inorganic chemicals, metals, pesticides, household chemicals, gasoline, motor oil, battery acid, roadway salt and other pollutants.
• Pathogens are disease-causing microorganisms present in human and animal waste. Most pathogens are bacteria.

Virginia's nonpoint source pollution prevention efforts focus on managing pathogens, nutrients and sediments because they pose the most significant threat to the health of our waterways, especially the Chesapeake Bay and its tributaries.

States are required to assess their waters and identify those adversely affected by nonpoint sources of pollution and then develop and implement a plan to address sources of nonpoint source pollution. States must also assist local governments, soil and water conservation districts and individuals in restoring, protecting and improving water quality through nonpoint source grants provided by the Environmental Protection Agency (EPA) and state resources. 

Steps to Help Control NPS Pollution

• Participate in planning and restoration opportunities in Virginia's Nonpoint Source Implementation program.
• Participate in one of Virginia's Watershed Roundtables .
• Participate in one of Virginia’s active Implementation Projects.
• Limit use of pesticides and fertilizer and use them at appropriate times of the year in recommended amounts. Contact a local extension agent for instructions.
• Participate in a stream cleanup program.
• Keep litter, pet wastes, leaves and debris out of street gutters and storm drains—these outlets drain directly to lake, streams, rivers and wetlands. Never directly deposit anything into a storm drain.
• Recycle grass clippings and leaves by mulching or composting.
• Pick up pet waste and bag it with regular household trash or use a backyard dog waste composter.
• Dispose of used oil, antifreeze, paints and other household chemicals properly, including accidental spills —do not deposit or wash waste into  storm sewers or drains.
• Make sure home septic system is working properly. Maintenance and prompt correction of problems are important.
• Plant a rain garden to catch and infiltrate excess storm water as it flows across your yard.
• Direct roof runoff onto a grassed area or into a rain barrel.
• Watch for soil erosion. Seed, install sod or plant ground cover to protect an eroded site.
• Use porous surfaces such as flagstone, gravel, stone and interlocking pavers rather than concrete or asphalt.