Pollutants

Nonpoint Source Pollution

Water pollution from diffuse sources across the landscape, including agricultural fields, lawns, streets, and construction sites, rather than from a single identifiable discharge point.

What It Means for Your Lake

Nonpoint source (NPS) pollution is contamination that reaches lakes and rivers from diffuse, widespread sources across the landscape rather than from a single pipe or discharge point. In Minnesota and Wisconsin, nonpoint source pollution is the dominant cause of lake water quality impairment, responsible for an estimated 80% to 90% of the phosphorus entering lakes. The major nonpoint sources include agricultural cropland (fertilizer, manure, and eroded soil), urban and suburban stormwater (lawn fertilizer, pet waste, road salt, and oil), construction sites (exposed soil and sediment), failing septic systems (phosphorus and pathogens), and atmospheric deposition (nitrogen and mercury). Unlike point source pollution from factories or wastewater treatment plants, nonpoint source pollution is extremely difficult to regulate because it originates from millions of individual sources across the landscape. Federal and state water quality regulations under the Clean Water Act have been highly effective at controlling point sources since the 1970s, but nonpoint source pollution has proven far more resistant to reduction. The Minnesota Pollution Control Agency has identified over 500 lakes as impaired by nutrient pollution, primarily from nonpoint sources. Addressing nonpoint source pollution requires a combination of voluntary conservation practices (cover crops, buffer strips, reduced tillage), regulatory programs (feedlot rules, stormwater permits, shoreland zoning), and financial incentives (cost-share programs, conservation easements). Progress is typically slow because reducing nonpoint source pollution requires changing land management practices across thousands of individual properties within a watershed.

Frequently Asked Questions