A recent forecast of the size of the “Dead Zone” in the northern Gulf of Mexico for late July 2019 reports that it will cover 8,717-square-miles of the bottom of the continental shelf off Louisiana and Texas. The unusually high Mississippi River discharge in May controls the size of this zone, which will likely be the second largest zone since systematic measurements began in 1985.
The water mass with oxygen concentrations less than 2 parts per million forms in bottom waters each year primarily as a result of nitrogen and phosphorus loading from the Mississippi River watershed, which fertilizes the Gulf of Mexico’s surface waters to create excessive amounts of algal biomass. The decomposition of this plant material in the bottom layer leads to oxygen loss.
Read more at Louisiana State University