Nutrients are chemical elements essential to plant and animal nutrition.
The two most common nutrients, nitrogen and phosphorus, are the major component of fertilizers for houseplants, lawns and gardens, and agricultural crops. While essential to life in small amounts, in high concentrations these nutrients are considered contaminants. In streams and reservoirs, an oversupply of nutrients leads to excessive growth of algae. Unsightly scums of algae on the surface of nutrient-enriched waters decrease recreational values and clog water intakes. Unseen problems occur as algae decay and decompose, removing most of the oxygen and making it difficult for fish and other aquatic life to survive.