Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. This often leads to excessive growth of algae (algal blooms). When these large algal blooms die, decomposer bacteria consume the dead organic matter. This decomposition process consumes large amounts of dissolved oxygen in the water, leading to a state of hypoxia (low oxygen) or anoxia (no oxygen). Fish and other aquatic organisms require dissolved oxygen to survive, so the depletion of oxygen leads to their death.