Stormwater Awareness Week: Stormwater Pollutants

Stormwater runoff flows off of impervious pavements and into storm drains, collecting pollutants as it travels. Any trash, debris, or chemicals that are lying on streets, rooftops, parking lots, or driveways will be carried by stormwater to storm drains and eventually to local waterways. When these pollutants enter our waterways, they threaten water quality, safe drinking water, and aquatic life. There are several pollutants that can be found in urban and suburban areas that can eventually make their way into streams and rivers through storm drains.


Silt fence covered in soil and rocks (sediment)

Some of the most common types of stormwater pollutants found in waterways include sediment, nutrients, microorganisms, oils and grease, metals, pesticides, and trash. Sediment is the most common pollutant that is found in our streams, rivers, and lakes. Sediment particles can be picked up when precipitation falls on exposed soils. Construction sites are a large source of sediment pollution, and when sites do not implement the proper sediment and erosion controls, then sediment can be carried off site and enter nearby waterways. Sediment is detrimental to aquatic life through interruption in important physiological processes processes including respiration and oxygen exchange across gills. Sediments can decrease light availability for plants by causing murky, cloudy waters. Sediments can also bind other pollutants including metals. Flashiness in urban streams following heavy rain events can cause stream erosion and increase sediment as well.


Nutrients including nitrogen and phosphorus are used as fertilizers in agricultural fields but are often found in stormwater runoff from urban areas. Fertilizers can be good for maintaining landscapes and for plant growth, but using too much or improper use can cause excess nutrients in runoff. Nutrients provide fuel for algal growth and when the algae die off they consume oxygen and deplete oxygen levels available for fish and other aquatic life. Certain algae can also produce toxins that are dangerous to pets and humans if ingested. This can cause issues with drinking water, especially up by Lake Erie that receives several algal blooms a year.


On top of harmful algal blooms producing toxins that can cause illnesses, microorganisms like bacteria and viruses in the water can also cause issues. These can cause impacts to aquatic life by decreasing oxygen and can also impair primary and secondary contact recreation, which means you cannot swim, boat, or wade in waterways with these warnings. Bacteria like E. Coli and other harmful pathogens can enter our waterways through leaking sanitary sewer lines, failing septic systems, and from waste such as pet waste that isn’t picked up.

Oily sheen in water found in stream between rocks

Oils and greases can come from several sources, such as poorly maintained cars, spills, vehicle accidents, restaurants, and waste oil disposal. Oils and greases typically leave an oily sheen on the surface of the water and can be toxic to aquatic organisms even in low concentrations.


Metals are also another harmful pollutant that can be toxic to aquatic life and can bioaccumulate in animals like fish. Metals like zinc, cadmium, lead, copper, and nickel are some commonly found metals. They can typically come from corroding, flaking, or decaying artificial surfaces that are found to contain metals or from automobiles or industrial sites.


Pesticides like herbicides, fungicides, and insecticides can be helpful in preventing unwanted pests, but can have adverse effects on the environment. When used excessively or improperly, pesticides can leach into storm drains and into local streams, rivers, and lakes. These can be toxic to aquatic life and even to other organisms that feed on the aquatic critters after the bioaccumulation of these toxins. Both pesticides and metals can also be harmful to drinking water quality.

illegal trash dumped on roadside

Trash and other debris that enters waterways through stormwater runoff can carry all of the aforementioned pollutants with them. Litter on the streets, animal waste, lawn clippings, woody debris, and more can impair habitat in streams and can break down, causing excess nutrient pollution and hazards to aquatic organisms.


Some other sources of pollutants include road salts, soapy wastewater from cleaning processes, and pool water discharge can also be harmful to aquatic life and water quality. All of the pollutants mentioned are illegal to dump down storm drains and if needed to be used, should be used according to their packaging and disposed of properly


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