When excess nutrients reach the Gulf of Mexico via the Mississippi-Atchafalaya River Basin, they stimulate an overgrowth of algae. When these algae die and decompose, they deplete oxygen in the water as they sink to the bottom. The resulting low oxygen levels cause motile animals, like fish and shrimp, to leave the area. Exposure to hypoxic waters has been found to alter fish diets, growth rates, reproduction, habitat use and the availability of commercially harvested species like shrimp.