From R. Eugene Turner and Nancy N. Rabalais

A hypoxic water mass with oxygen concentrations ≤ 2 mg l-1 forms in bottom waters of
the northern Gulf of Mexico continental shelf each year. Nutrients from the Mississippi River
watershed, particularly nitrogen and phosphorus, fertilize the Gulf’s surface waters to create
excessive amounts of algal biomass, whose decomposition in the bottom layer leads to oxygen
distress and even organism death in the Gulf’s richest waters. These low oxygen conditions
threaten living resources including humans that depend on the fish, shrimp and crabs that are
caught there. Various models use the May nitrogen load of the Mississippi River as the main
driving force to predict the size of this hypoxic zone in late July. Our prediction is based on these
The June 2018 forecast of the size of the hypoxic zone in the northern Gulf of Mexico for
late July 2018 is that it will cover 17,250 km2 (6,620 mi2) of the bottom of the continental shelf
off Louisiana and Texas. The 95% confidence interval is that it will be between 14,628 and
19,727 km2 (5,648 and 7,617 mi2). This estimate is based on the assumption that there are no
significant tropical storms occurring in the two weeks before the monitoring cruise, or during the
cruise. If a storm does occur, then the size of the zone is predicted to be 70% of the predicted
size without the storm, equivalent to 12,075 km2 (6,316 mi2).