Nitrogen is very common and found in many forms in the environment. Nitrogen is most abundant in its molecular form (N₂^-) which makes up 79 percent of the air we breathe. In this form, nitrogen is useless to most plants and animals. Blue-green bacteria, the most common algae found in algae blooms, can convert nitrogen (N₂^-) into other compounds such as ammonia (NH₃) and nitrates (NO₃^-) which can be used by plants in order grow. Nitrogen is a common ingredient found in most fertilizers.

Animals get the nitrogen they need by eating plants or by eating animals that have eaten plants. Animal digestive systems break down plant proteins to form nitrogen compounds which can be used to form the proteins they need. Much nitrogen is released in the wastes produced by animals. Ducks and geese contribute a heavy load of nitrogen (from excrement) in areas where they are plentiful.

When plants and animals die, proteins are broken down by bacteria forming ammonia (NH₃). Ammonia is broken down by other bacteria to form nitrite (NO₂^-). Ammonia and nitrite are both poisonous to animals. Nitrite is then consumed by a third type of bacteria which forms nitrates (NO₃^-). Nitrates can then be used by plants in order to grow. This recycling of nitrogen through the environment is called the nitrogen cycle.

Nitrate is a major ingredient in most fertilizers. When it rains, varying amounts of nitrates wash from farmlands and lawns into nearby streams. Nitrates can also enter streams from animal wastes, leaking septic systems, and sewage.

Nitrate (NO₃^-) can be harmful to humans. It is broken down in our intestines becoming nitrite (NO₂-). Nitrite affects the ability of red blood cells to carry oxygen. If infants consume water high in nitrite/nitrates, they may suffer from a serious condition called methemoglobinemia or "blue baby" disease. Wells contaminated by sewage or agricultural run off are a major concern in some areas. Nitrites can also cause serious illnesses in fish.