An oxygen-starved hypoxic zone, commonly called a dead zone and shown in red, forms each summer in the Gulf of Mexico. Fish and shellfish either leave the oxygen-depleted waters or die, resulting in losses to commercial and sports fisheries.
A dead zone-causing algal bloom stained the Gulf of Mexico green in 2007.
Credit Donald Scavia / Univ. of Michigan
Farmland runoff containing fertilizers and livestock waste, some of it from as far away as the Corn Belt, is the main source of the nitrogen and phosphorus that cause the annual Gulf of Mexico "dead zone."