We often hear about oil spills or toxic waste sites, where the source of pollution is easily identified. However, with nonpoint source (NPS) pollution, it’s not possible to pinpoint a specific pipe or factory that is spewing toxins into the environment, as the pollution originates from diffuse runoff across landscapes.
Water is great for cleaning clothes or dishes because it suspends unwanted particles and takes them down the drain. Unfortunately, water does the same with pollutants, contaminating lakes, rivers, oceans, and groundwater. NPS pollution occurs when rain or snowmelt picks up pollutants such as fertilizers, pesticides, oils, and microplastics and carries them into creeks, rivers, lakes, and groundwater. As runoff flows, accumulating everything in its path, the results can be detrimental to watersheds nationwide.
According to the U.S. Environmental Protection Agency, nonpoint source pollution remains the leading cause of water quality issues nationwide. Nutrient and sediment runoff from agriculture tops the list, according to the Center for American Progress. The EPA’s Section 319 monitoring program continues to evaluate strategies in real-world watershed projects, as of the latest update in early 2025.
On the public health front, nitrites from fertilizer can lead to conditions like “blue baby syndrome” and hypertension. Raunoff pesticides and herbicides carry carcinogenic risks and fuel toxic algal blooms. According to researchers at the University of Missouri, NPS pollution is also a significant threat to safe drinking water. Although the Clean Water Act has successfully reduced significant pollution at its source, it has had little impact on curbing NPS pollution.
“Large amounts of nitrates and nitrites, such as those found in fertilizer, can cause negative health effects such as blue baby syndrome,” said Robin Rotman, assistant professor at the MU School of Natural Resources. “Nonpoint source pollution can lead to toxic algae blooms; pesticides and herbicides also contain carcinogens that can threaten human health.”
Because preventing NPS pollution is critical for promoting water quality and protecting wildlife, it is vital to address. Let’s examine common sources so we can identify opportunities to mitigate them.
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Lawn, Garden & Agricultural Chemicals
Fertilizers commonly find their way to waterways, promoting the growth of microorganisms and causing dissolved oxygen levels to plummet. Without sufficient oxygen, fish and other aquatic species suffocate. Likewise, pesticides also wash into waterways, making the water unfit for human consumption and unsafe for wildlife.
What to Do:
- Adopt regenerative or organic gardening: use compost, seaweed, or biochar instead of synthetic fertilizers.
- Practice non-toxic, integrated pest management: target pests with pesticides only when necessary, and choose beneficial insects over chemical pesticides. Seek out natural fertilizers and soil amendments such as compost and seaweed. Additionally, whenever possible, opt for organic foods to reduce the use of pesticides and synthetic fertilizers on farms.
- Farms can utilize prairie filter strips, a conservation approach that involves planting rows of perennial wildflowers and grasses six to 18 feet wide. Research shows that these strips can reduce nitrates by ~35%, total nitrogen by up to 73%, and phosphorus by 82%—even at narrow widths.
Household Chemicals & Vehicle Washing
Some households dispose of chemicals such as paint, used oil, antifreeze, drain cleaner, ammonia, bleach, upholstery cleaner, swimming pool chemicals, and other household chemicals down storm drains. This practice pollutes water supplies since storm sewers typically lead directly to lakes, rivers, and wetlands without being treated. Additionally, de-icing salts wash into waterways, harming plants and aquatic life.
Likewise, washing a car at home has the same effect because all the cleaning products, grime, and oil typically end up in the stormwater system without being adequately treated. Again, this wreaks havoc on ecosystems and causes toxins to accumulate.
What to Do:
Litter, Pet Waste & Microplastics
Street litter regularly makes its way into stormwater drains, reaching rivers, lakes, and the oceans; tons of plastic waste end up in our oceans every year. Unmanaged pet waste will also wash into our waterways. Even laundering synthetic fabrics causes microplastics to enter waterways through discharge water.
What to Do:
Stormwater Surges from Impervious Surfaces
Impervious surfaces, such as parking lots, roads, compacted gravel, buildings, and other built surfaces, often cause stormwater surges that lead to more polluted runoff. Unfortunately, it is challenging to prevent all sources of nonpoint source pollution, including those from cars, neighbors, and construction sites. Nevertheless, you can reduce runoff from your property.
What to Do:
- Replace or supplement impervious surfaces with permeable pavements: Choose porous concrete, asphalt, or interlocking pavers to filter water on-site.
- Install rain gardens, bioswales, or constructed wetlands: these attractive natural features can slow and filter runoff. Please encourage others to use them by sharing your experience in your community and speaking with your local government or your employer.
- Remember that roofs also create runoff: Plant a green roof, use rain barrels, or plant a rain garden to help prevent runoff, thermal pollution in waterways, and stormwater surges.
Prioritize Low-Hanging Fruit First
The urgency of NPS pollution concerns has only increased, but mitigation solutions at the household and community scale are well-defined and cost-effective. Whether you’re planting native shrubs or pushing your town to adopt bioswales, these incremental steps matter. Start your changes with high-impact, low-cost actions on your property, then gradually add larger infrastructure features such as permeable paving and bioswales. Eventually, we can have an infrastructure that secures water quality for people and ecosystems.
Editor’s Note: This article was originally published on January 18, 2022, and substantially updated in July 2025..