Found naturally in waterways but excessive amounts causes problems.
Process is called nitrogen fixation .
Aquatic animals obtain nitrogen by either consuming aquatic plants, or consuming those animals that consume the plants Nitrates can be returned to the soil from animal urine, feces, carcass decay, and plant decay. High levels of nitrates or phosphates stimulate algae and aquatic plant growth. Aerobic bacteria populations then increase because of the large amounts of organic matter now available in the water. The resulting elevated bacteria populations deplete much of the dissolved oxygen found in the water. Nitrates also react directly with hemoglobin in human blood and other warm-blooded animals to produce methemoglobin.