NOAA scientists are forecasting this summer’s Gulf of Mexico hypoxic area or “dead zone” — an area of low to no oxygen that can kill fish and other marine life — to be approximately 4,880 square miles. The 2021 forecasted area is smaller than, but close to the five-year average measured size of 5,400 square miles.
This forecasted size is also substantially less than the 8,776-square-mile 2017 Gulf hypoxic zone, which was the largest zone measured since mapping began in 1985. The annual prediction is based on a suite of models that incorporate U.S. Geological Survey (USGS) river-flow and nutrient data.
“Understanding the effects of hypoxia on valuable Gulf of Mexico resources has been a long-term focus of NOAA’s research,” said Nicole LeBoeuf, acting director of NOAA’s National Ocean Service. “These forecasting models inform us of the potential magnitude of the Gulf of Mexico hypoxic zone that might impact living marine resources and coastal economies.”
The annual Gulf of Mexico dead zone is primarily caused by excess nutrient pollution from human activities in urban and agricultural areas throughout the Mississippi River watershed. When the excess nutrients reach the Gulf, they stimulate an overgrowth of algae, which eventually die and decompose, depleting oxygen as they sink to the bottom. The resulting low oxygen levels near the bottom of the Gulf cannot support most marine life. Fish, shrimp and crabs often swim out of the area, but animals that are unable to swim or move away are stressed or killed by the low oxygen. The Gulf of Mexico dead zone occurs every summer.