The Gulf of Mexico's dead zone is expected to be larger than average in 2011 because of the extreme flooding of the Mississippi River, an annual forecast said.

The forecast by a team of NOAA-supported scientists from the Louisiana Universities Marine Consortium, Louisiana State University and the University of Michigan predicts the area could measure 8,500- to 9,421 square miles, an area about the size of New Hampshire, the National Oceanic and Atmospheric Administration said Tuesday in a release.

The forecast is based on Mississippi River nutrient inputs compiled by the U.S. Geological Survey.

Hypoxia is caused by excessive nutrient pollution, often from human activities such as agriculture, that results in too little oxygen to support most marine life in bottom and near-bottom water.

"This ecological forecast is a good example of NOAA applied science," said Jane Lubchenco, undersecretary of commerce for oceans and atmosphere and NOAA administrator. "While there is some uncertainty regarding the size, position and timing of this year's hypoxic zone in the gulf, the forecast models are in overall agreement that hypoxia will be larger than we have typically seen in recent years."

The average over the past five years is approximately 6,000 square miles of impacted waters, considerably larger than the 1,900-square-mile target set by the Gulf of Mexico-Mississippi River Watershed Nutrient Task Force, NOAA officials said.

The largest hypoxic zone measured to date was in 2002 and encompassed more than 8,400 square miles, NOAA said.