Predictive models of hypoxia in the Gulf of Mexico suggested the dead zone would range in size from 7,286 to 8,561 square miles. Instead, a July survey group measured the zone to be 5,840 square miles, about the state of Connecticut.
According to NOAA: Hypoxia [low oxygen] is fueled by nutrient runoff from agricultural and other human activities in the watershed. These nutrients stimulate an overgrowth of algae that sinks, decomposes and consumes most of the oxygen needed to support life. Normally the low or no oxygen area is found closer to the Gulf floor as the decaying algae settle towards the bottom. This year researchers found many areas across the Gulf where oxygen conditions were severely low at the bottom and animals normally found at the seabed were swimming at the surface.