NEW ORLEANS (AP) — This year's "dead zone" at the bottom of the Gulf of Mexico, caused largely by fertilizer runoff from U.S. farms, is bigger than average but doesn't approach record size as scientists had predicted, according to findings released Monday.

The area of low oxygen covers 5,840 square miles (15,125 sq. kilometers) of the Gulf floor, said scientists led by Nancy Rabalais of the Louisiana Universities Marine Consortium.

The low oxygen kills animals that cannot swim away, such as worms, starfish, small burrowing shrimp and some crabs, hurting food quality for fish that return when oxygen levels rise, she wrote in her annual report.

The dead zone is caused when nitrogen and phosphorus, much of it from farm fertilizer in the 41-state Mississippi River basin, feed algae blooms at the river's mouth. Algae and the protozoa that eat them die and fall to the bottom, where their decomposition uses up oxygen.

Scientists from Louisiana State University and the University of Michigan had expected a wet spring to bring more nutrients than usual down the Mississippi River, leading to a dead zone that could have approached or exceeded the largest ever. The largest dead zone on record was in 2002, when it spread across 8,481 square miles (21,900 sq. kilometers) of the Gulf.

The Mississippi River Collaborative, a partnership of environmental organizations and legal centers in states along the Mississippi River, sued the U.S. Environmental Protection Agency last year, calling for it to set standards for nitrogen and phosphorus pollution and make states meet them.

"EPA told states to develop numeric nitrogen and phosphorus limits 15 years ago," Cynthia Sarthou, executive director for the Gulf Restoration Network, a coalition member, said in a news release. "EPA has spent the decade and a half since backing off hard deadline after hard deadline for reducing dead zone-causing pollution."

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Online:

Gulf of Mexico hypoxia: http://www.gulfhypoxia.net/default.asp