Runoff is water from rain or melted snow which is not absorbed and held by the soil, but runs over the ground and through loose soil. Agricultural runoff is water leaving farm fields because of rain, melted snow, or irrigation. As runoff moves, it picks up and carries pollution, which it can deposit into ponds, lakes, coastal waters, and underground sources of drinking water. 

Agricultural runoff can include pollution from soil erosion, feeding operations, grazing, plowing, animal waste, application of pesticides, irrigation water, and fertilizer. Pollutants from farming include soil particles, pesticides, herbicides, heavy metals, salts, and nutrients such as nitrogen and phosphorus. High levels of nitrates from fertilizers in runoff can contaminate drinking water and cause potentially fatal "blue baby" syndrome in very young infants by disrupting oxygen flow in the blood. 

Polluted agricultural runoff is the leading source of water pollution in rivers and lakes, according to a federal report. It can also trigger algae blooms in coastal waters, and produce "dead zones" in the ocean where there is no oxygen and few fish or wildlife can survive. In cities and suburbs, urban and industrial runoff is also a major source of water pollution. 

Agricultural runoff can create a bad taste and odor in drinking water and contaminate drinking water, well water, and food sources. The pesticides in runoff can accumulate in fish, which can expose people who eat the fish to high levels of these chemicals.

This description is based on the information found in the Web links listed with this topic.

Web Links from MedlinePlus (National Library of Medicine)
Drinking Water
Environmental Health
Hazardous Waste
Water Pollution

More Links
Agriculture: Polluted Runoff (Environmental Protection Agency)
Improving Old MacDonald's Farm: Protecting Streams from "Fruited Plains" (Environmental Protection Agency) (PDF — 151 KB)
Protecting Water Quality from Agricultural Runoff (Environmental Protection Agency) (PDF — 119.3 KB)

Chemicals in Ag Runoff
Are these chemicals in MY community?
Acetone
Ammonia
Cadmium
Diesel
Endocrine Disruptors
Gasoline
Methanol
Particulate Matter
Persistent Organic Pollutants (POPs)
Pesticides
Polycyclic Aromatic Hydrocarbons (PAHs)
Polyvinyl Chloride (PVC)
Solvents
Volatile Organic Compounds (VOCs)

Last Updated: October 16, 2012