(The Center Square) − The Gulf of America’s “dead zone” has shrunk significantly this summer, with scientists measuring a hypoxic area of just over 4,400 square miles — roughly a third smaller than last year and far less than the long-term average, federal officials announced Wednesday.

The dead zone, a stretch of oxygen-depleted water that forms annually off the Louisiana and Texas coasts, is caused primarily by excess nutrients washing into the Gulf from the Mississippi-Atchafalaya River Basin.

This year’s zone, measured during a July 20–25 survey aboard the research vessel Pelican, was 4,402 square miles — 21% smaller than NOAA’s early-season estimate and the 15th smallest on record, according to NOAA-supported scientists from LSU and the Louisiana Universities Marine Consortium.

“This year’s significant reduction in the Gulf of America’s ‘dead zone’ is an encouraging sign for the future of this area,” said Laura Grimm, acting NOAA administrator. “It highlights the dedication and impactful work of NOAA-supported scientists and partners, and serves as a testament to the effectiveness of collaborative efforts in supporting our U.S. fishermen, coastal communities, and vital marine ecosystems.”

The measured area is equivalent to roughly 2.8 million acres of bottom habitat temporarily made unavailable to marine life such as fish and shrimp due to low oxygen levels.

That marks a 30% drop from 2024, when the zone spanned a massive 6,703 square miles — more than 1.3 times the long-term average and nearly 3.5 times larger than the target goal of 1,930 square miles set by the Mississippi River/Gulf of Mexico Hypoxia Task Force.

Despite this year’s improvement, the five-year running average remains high at 4,755 square miles—still more than double the federal benchmark.

Dead zones emerge when excess nutrients — mostly nitrogen and phosphorus from upstream agriculture and wastewater — fuel algae blooms. As algae die and sink, their decomposition consumes oxygen in bottom waters. Without sufficient oxygen, marine species must flee or perish.

In 2024, the area west of the Mississippi River experienced heavy hypoxia with extremely low oxygen readings and little water mixing, according to NOAA.

“The stratification of warmer surface water over cooler, saltier bottom water was strong enough to prevent oxygen replenishment,” researchers wrote in a followup report.

Some bottom waters saw oxygen drop across the lower five meters of the water column.

Even with relatively low chlorophyll readings — indicating modest live algae near the surface — researchers noted high concentrations of degraded algae and organic detritus near the seafloor, still enough to drive significant bacterial oxygen consumption.

The Mississippi River/Gulf of Mexico Hypoxia Task Force, a coalition of federal and state agencies, has worked for over two decades to reduce nutrient pollution flowing into the Gulf. The EPA established a dedicated Gulf Hypoxia Program in 2022 to accelerate these efforts.

“The Gulf of America is a national treasure that supports energy dominance, commercial fishing, American industry, and the recreation economy,” said Peggy Browne, acting assistant administrator for the EPA’s Office of Water. “I look forward to co-leading the work of the Gulf Hypoxia Task Force to assess evolving science and address nutrient loads from all sources.”

So far, nitrogen loading from the Mississippi River has not declined since the 2001 adoption of the Hypoxia Action Plan, scientists noted. NOAA’s June 2025 forecast, which had predicted a dead zone of 5,574 square miles, was based on U.S. Geological Survey nutrient data from spring river flows and fell within model uncertainty ranges.

NOAA’s Coastal Hypoxia Research, Ocean Technology Transition, and Uncrewed Systems programs are working to improve monitoring and prediction tools. This year, several autonomous surface vehicles were deployed alongside ship-based crews to compare mapping methods.

Researchers said ASVs may provide a more cost-effective way to track dead zones in the future. NOAA also partners with the Northern Gulf Institute and Gulf of Mexico Alliance to expand observational capabilities and state-level technical support.