Aquatic life uses may be hampered when the entire water body experiences daily fluctuations in dissolved oxygen levels as a result of nightly plant respiration. Extreme oxygen depletion can lead to death of desirable fish species. Additional nitrate sources include excreta both from wild animals in the surrounding watersheds, excreta from wildfowl congregating on the water body and boats that discharge raw sewage overboard. Industries that use nitrates in manufacturing may release nitrate in the effluent water. The primary nitrogen source in the western United States is agricultural fertilizers.
Atmospheric deposition is the second-most prevalent source.
The central and southeastern United States also primarily derive nitrogen pollution from agricultural fertilizers. The second-most prevalent source is animal manure. Overland flow is the most direct route for water transportation. Underground flow is less direct because water flow is impeded by soil permeability and porosity constraints. The combustion of fossil fuels and the discharge of agricultural and industrial nitrogen-containing compounds into the atmosphere has allowed gases, aerosols, and fine particles to be borne by wind and deposited either directly into the water body or carried from the atmosphere to the water body via precipitation.