Polluted stormwater runoff can have many adverse effects on plants, fish, animals, and people, including:
Bacteria and other pathogens can wash into swimming areas and create health hazards, often making beach closures necessary.
Debris - plastic bags, 6-pack rings, bottles, and cigarette butts - washed into waterbodies can choke, suffocate, or disable aquatic life like ducks, fish, turtles, and birds.
Excess nutrients can cause algae blooms. Then, when the 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.
Household hazardous wastes like insecticides, pesticides, paint, solvents, used motor oil, and other auto fluids can poison aquatic life. Land animals and people can become sick from eating diseased fish and shellfish or ingesting polluted water.
Polluted stormwater often affects drinking water sources. This, in turn, can affect human health and increase drinking water treatment costs.
Sediment can cloud the water and make it difficult or impossible for aquatic plants to grown.