Nitrogen is an element needed by all plants and animals to build protein. Ammonia is also released as bacteria break down aquatic plant and animal remains. Excretions of aquatic organisms are very rich in ammonia. In large groups, duck and geese can contribute heavy loads. Nitrogen in the forms of ammonia and nitrates functions as a plant nutrient and initiates eutrophication .
Sewage is the main source of human-influenced nitrate addition to streams.
Nitrates are introduced by inadequately treated wastewater from sewage treatment plants, effluent from illegal sanitary sewer connections, and poorly functioning septic systems. Fertilizers from fields and runoff from cattle feedlots, dairies, and barnyards are other nitrate sources. Phosphates accumulate from living plants and animals, their byproducts, and their remains. Phosphate ions bonded to soil particles and in laundry detergents also end up in streams. Other sources of phosphorus include sewage, animal waste, soil erosion, fertilizers, and drained swamps and marshlands.