Researchers supported by the National Oceanographic and Atmospheric Administration said the 2013 oxygen-free or hypoxic "dead" zone measures 5,840 square miles, an area the size of Connecticut. They said it shows nutrients from the Mississippi River watershed are affecting the nation's commercial and recreational marine resources in the gulf.
Models had predicted the gulf hypoxic zone would range in size from 7,286 to 8,561 square miles.
Nutrients from agricultural runoff and other human activities stimulate an overgrowth of algae in the gulf that sinks, decomposes and consumes most of the oxygen needed to support life.
"A near-record area was expected because of wet spring conditions in the Mississippi watershed and the resultant high river flows, which deliver large amounts of nutrients," Nancy Rabalais, executive director of the Louisiana Universities Marine Consortium, said. "But nature's wind-mixing events and winds forcing the mass of low oxygen water towards the east resulted in a slightly above average bottom footprint."
The hypoxic zone that forms each summer threatens valuable commercial and recreational gulf fisheries that in 2011 had a commercial dockside value of $818 million, researchers said.