An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Nutrient Pollution

The Effects: Environment

Dead fish floating on the surface of algal polluted water
Algal blooms can reduce the ability of fish and other aquatic life to find food and can cause entire populations to leave an area or even die.
Aerial view of algal polluted river
Harmful algal blooms cause thick, green muck that impacts clear water, recreation, businesses and property values.

Nutrient pollution fuels the growth of harmful algal blooms which have negative impacts on aquatic ecosystems.

Direct exposure to algae

Harmful algal blooms sometimes create toxins that are detrimental to fish and other animals. After being consumed by small fish and shellfish, these toxins move up the food chain and can impact larger animals like sea lions, turtles, dolphins, birds and manatees.

Even if algal blooms are not toxic, they can negatively impact aquatic life by blocking out sunlight and clogging fish gills.

Dead zones and hypoxia

Nutrient pollution can create dead zones - areas in water with little or no oxygen - where aquatic life cannot survive. Also known as hypoxia, these areas are caused by algal blooms consuming oxygen as they die and decompose. Aquatic animals - particularly young fish and seafloor dwellers like crabs and clams - must leave the affected area to survive. 

Over 166 dead zones have been documented nationwide, affecting waterbodies like the Chesapeake Bay and the Gulf of Mexico. The Gulf of Mexico dead zone is the largest in the United States, measured to be 5,840 square miles in 2013. It occurs every summer because of nutrient pollution from the Mississippi River Basin, an area that drains 31 upstream states. The Mississippi River/Gulf of Mexico Hypoxia Task Force coordinates nutrient management in this area.

Acid rain

Acid rain, caused by nutrient pollution in the air, damages lakes, streams, estuaries, forests and grasslands across the country.

Air pollution

Airborne nitrogen compounds like nitrogen oxides contribute to the formation of other air pollutants such as ground-level ozone, a component of smog which can restrict visibility. Wind and weather can carry ozone many miles from urban to rural areas. Ozone pollution can damage trees and harm the appearance of vegetation and scenic areas.