Mississippi scientists are watching for the possible spread of an area of oxygen-depleted water off the Louisiana coast that could move eastward.

A recently released study suggests the dead zone could be more than 10,000 square miles this summer. It has averaged about 6,000 square miles since 1990.

The dead zone forms as substances from farms, such as nitrogen and phosphorous, travel down the Mississippi River or one of its tributaries and into the Gulf of Mexico.

The fertilizers, which help plants grow on land, cause algae to grow in the water. The algae deplete the oxygen, causing a dead zone at the bottom of the water.

Dead zones disperse what marine life can swim away and kill what cannot.

Scientists expect flooding along the Mississippi River will bring higher levels of fertilizer into the Gulf.

“We’ve seen it change in places in Europe, and it’s been a disaster. We’re fooling around with a third of the U.S. fisheries,” said R. Eugene Turner, an LSU coastal ecology professor.

Dead zones also cause red tides, which could kill lots of fish and hurt tourism on the coast.

“Off the coast of Louisiana, there’s a huge area where you can’t catch fish,” said Nancy Rabalais, executive director of the Louisiana Universities Marine Consortium, or LUMCON. “The same thing could happen off Mississippi. They have lots of reefs, and there are die-offs around these artificial reefs.”

Researchers have been studying it since the 1970s.

Steven Lohrenz, chairman of the University of Southern Mississippi’s Department of Marine Science, said USM has done several cruises to examine oxygen near the barrier islands off the Mississippi shore.

He said two dead zones in the region — one near the barrier islands and one near the Mississippi River delta — are not as serious as the dead zone in Louisiana.

“Whether we see something on the Gulf Coast or some kind of algal bloom is unknown,” Lohrenz said. “We don’t understand shelf ecosystems enough (in Mississippi) to say why its occurring.”

The EPA’s Mississippi River/Gulf of Mexico Watershed Nutrient Task Force has asked 31 states to better monitor nutrients released into the river and its tributaries. Last week, the EPA would award $4.2 million to people interested in adopting programs that would reduce nutrients in target areas along the Mississippi and Ohio rivers.

The dead-zone forecast is based on nitrate levels in the Mississippi River in Baton Rouge, La. A follow-up forecast will be made in July, Rabalais said.

“By that time, we should see that influence of all the freshwater in the Gulf,” Rabalais said.

Rabalais said she does not expect the Mississippi River to crest in Louisiana as it has in Midwest states during recent flooding there.