The hypoxic zone in the Gulf of Mexico forms every summer and is a result of excess nutrients from the Mississippi River and seasonal stratification (layering) of waters in the Gulf. Nutrient-laden freshwater from the Mississippi River flows into the Gulf of Mexico. This freshwater is less dense and remains above the more dense saline Gulf water. In addition to the saline gradient caused where the freshwater and saline water meet, the freshwater is warmer than the deeper ocean water, further contributing to the stratification. This stratification prevents the mixing of oxygen-rich surface water with oxygen-poor water on the bottom of the Gulf. Without mixing, oxygen in the bottom water is limited and the hypoxic condition remains.