When nutrients wash into waterways through storm runoff, they deplete oxygen in the water that fish need to survive.
Nitrogen and phosphorus typically enter streams and lakes from fertilizers, dog waste, and other sources. Over time, these nutrients build up in the water and promote algae and water plant growth, and as they decay, they lower oxygen levels in the water.
Algal blooms can be harmful to fish as they feed upon algae, toxins accumulate within the fish, and when a predator fish consumes that fish, they too are consuming higher toxin levels.
Pesticides and heavy metals that enter waterways can also harm or kill fish. Synthetic pesticides used for weed and bug control are toxic in even small amounts.
Heavy metals created when fossil fuels are burned enter the atmosphere, eventually making their way into bodies of water.
Exposure to heavy metals can impair a fish’s ability to smell, disrupting its ability to locate food and protect itself from predatory animals and fish.