It used to be that the low-oxygen “dead zone” in the northern Gulf of Mexico was described as being the size of New Jersey.

But no more. This summer, scientists said the dead zone off the Louisiana Coast surpassed 8,000 square miles.

“Now it’s approaching the size of Massachusetts,” said Nancy Rabalais, chief scientist with the Louisiana Universities Marine Consortium, who has been monitoring the dead zone for years.

The previous record was 7,728 square miles in 1999.

But Rabalais said this year’s estimate is low because the area of low oxygen water stretched from the Louisiana coast well into Texas. “Because of time constraints, we weren’t able to map the entire extent into Texas,” Rabalais said.

Although the Gulf appears to be an immense area, coastal currents actually trap the Mississippi River discharge in a narrow area that flows westward along the coast, preventing nutrient laden water from being diluted with the rest of the Gulf.

The dead zone is created as river flows in the late spring and summer form a fresh water layer above the more salty Gulf water along the coast. The excess nutrients carried with the river water spur huge amounts of algae growth when they reach the Gulf. As the algae die, they sink and decompose in a process that depletes the lower, saltier layer, of oxygen.

When flows from the Mississippi River are strong, as they were this year, the top and bottom layers can’t mix, preventing oxygen from being resupplied to the bottom.

Recent studies in the Gulf have shown the situation has gotten worse since the 1950s as the amount of nutrients flowing out the Mississippi River has dramatically increased.

While the Gulf and the Chesapeake have similar problems, the Gulf’s is on a massive scale. The most important river, the Mississippi, drains a basin that covers all or part of 31 states, including major agricultural centers in the Midwest.

State and federal officials this year signed an action plan which called for reducing the amount of nitrogen discharged from the Mississippi River by 30 percent over 15 years.

But the plan, which emphasized the control of agricultural runoff, the restoration of wetlands and the planting of stream buffers, was expected to cost more than $1 billion a year. Implementation is contingent on federal support.

Some worry that this could mean the Mississippi basin would compete with the Bay watershed for funding, but others see the Chesapeake region — which has been working to reduce nutrient pollution since 1987 — as a model for efforts that could be used in the Mississippi and other places.

“Much of what we are doing, and the things that we are learning, will work just as well in the Mississippi River basin as they do in the Chesapeake Bay basin,” said Tom Simpson, of the University of Maryland’s College of Agriculture and Natural Resources. “We are a good pilot program for things that can be transferred there.”

EPA Administrator Christie Whitman made a similar point when visiting the Bay Program this summer. During a meeting with the Citizens Advisory Committee, she cited the Gulf of Mexico’s dead zone problem as an example of an area that could benefit from lessons learned in the Bay.

“I think you can really provide us with a template as we focus our efforts on how to move forward to try to address some of these other, and bigger, issues,” she said