The most common NPS pollutants are soils (sediment) and nutrients picked up by runoff as it flows over land to surface waters. These pollutants may come from agricultural land and other open spaces, urban areas, construction sites, roads, parking lots, etc. Other common NPS pollutants include pesticides, pathogens (bacteria and viruses), salts, oil and grease.

Soil Erosion From Farm Field

Sediment Runoff From Construction Site (Courtesy NRCS)

In Iowa, sediment is the leading nonpoint source pollutant. Most of the streams and lakes in Iowa are negatively impacted by sediment/siltation. In Iowa, most sediment comes from agricultural practices such as cropland tillage and livestock in pastures, woodlands and feedlots. High levels of sediment also erode and are deposited in waterbodies from construction sites, streambanks and lake shorelines.

Large Gully in a Farm Field	Streambank Erosion
Erosion Threatening Bridge Structure	Sediment Washing Into a River

Nutrients, especially nitrogen and phosphorus, are other main NPS pollutants in Iowa. As nutrient criteria are developed, it is expected that many of the waterbodies in Iowa will be impaired based on nutrient loading. Nutrients can come from fertilizers (both on agricultural land and on residential lawns, golfcourses, etc.) and from organic sources such as manure and human sewage.

Cattle in a Stream Deposit Sediment and Manure Directly into the Stream

Water is Green from Excess Nutrients Algae in Stream From Excess Nutrients

NPS pollution is responsible for sediment that fills in lakes and streams, covers fish habitat, and reduces visibility in the water. It is also often responsible for beach closures, destroyed fish and wildlife habitat, unsafe drinking water, fish kills, and reduced aesthetic and recreational value of waterbodies. Bacteria from manure or human sewage can cause health problems. Excessive nutrients in water from either chemical fertilizer or organic matter (including manure) can cause algae blooms in lakes, sometimes making lakes smelly and boating difficult. High levels of nutrients in waterbodies can also cause fish kills, by decreasing dissolved oxygen in lakes and streams. Excessive agricultural or lawn chemicals can also cause the water to be unfit for drinking, or require additional and costly treatment.

Fish Kill

Pesticides and Fertilizers Applied to Lawns can Cause NPS Pollution if Applied Excessively or Near Waterbodies

DNR Contact
Steve Hopkins
DNR Nonpoint Source Program Coordinator
(515) 281-6402
Stephen.Hopkins@dnr.iowa.gov