What is Stormwater?

When precipitation (rain or snow melt) falls on hard surfaces such as roads, sidewalks, driveways, and roofs, it can’t soak into the ground. Instead, it runs off the surface and often makes it’s way to the storm drain system. This runoff is referred to as “stormwater.”

If stormwater is polluted by materials left on the ground (such as pet waste, fertilizer, pesticides, ice melt, motor oil, driveway sealer, cigarette butts, etc.), that pollution is also carried to the nearest waterway.

Polluted stormwater often affects drinking water sources, which can affect human health and increase drinking water treatment costs.

Additional problems stemming from stormwater pollution include:

  • Sediment that can cloud the water and make it difficult or impossible for aquatic plants to grow. Sediment also can destroy aquatic habitats.
  • Excess nutrients that can cause algae blooms. When algae die, they sink to the bottom and decompose in a process that removes oxygen from the water. Fish and other aquatic organisms can’t exist in water with low dissolved oxygen levels.
  • Bacteria and other pathogens that can wash into swimming areas and create health hazards, often making beach closures necessary.
  • Debris—plastic bags, six-pack rings, bottles, and cigarette butts—washed into waterbodies can choke, suffocate, or disable aquatic life like ducks, fish, turtles, and birds.
  • Household hazardous wastes like insecticides, pesticides, paint, solvents, used motor oil, and other auto fluids that can poison aquatic life. Land animals and people can become sick or die from eating diseased fish and shellfish or ingesting polluted water.

Polluted stormwater runoff causes more than half of the pollution in our waterways, according to the U.S. Environmental Protection Agency.

Our storm drain systems are a network of pipes that collect stormwater runoff and route it directly to the nearest waterway. This pipe system has no treatment or filtration of any kind.


Watch the video to see how stormwater pollution spreads.