Eutrophication is a process whereby water bodies, such as lakes, estuaries or slow moving streams, accumulate nutrients that stimulate excessive algal growth. Nutrients can come from many sources, such as: 1)fertilizers applied to agricultural fields, golf courses and suburban lawns; 2) deposition of nitrogen from the atmosphere; 3) erosion of soil containing nutrients; 4) sewage treatment plant discharges; and 5) the burning of fossil fuels. As the algae grow faster, they shade existing plants until both the algae and some plants die off. As the dead algae and plants are decomposed by microbes, dissolved oxygen is used up, creating an anoxic condition - an environment without oxygen. Such an environment becomes unsuitable for plants and animal life. Algal blooms also lead to oxygen depletion resulting in fish population decline and the creation of aquatic conditions that can be harmful to human health.