NOAA scientists have forecast that the annual “dead zone” in the Gulf of Mexico, currently referred to as the Gulf of America by the U.S. government, will be 5,574 square miles – just slightly higher than the long-term average of 5,244 square miles.
The dead zone is a massive hypoxic area caused by excess nutrient pollution and other discharges into the Mississippi-Atchafalaya watershed, which feeds algae growth in the Gulf of Mexico.
“When these algae die and decompose, they deplete oxygen in the water as they sink to the bottom,” NOAA's National Ocean Service said in a release. “Large dead zones lead to extensive habitat loss for several ecologically and economically important species in the Gulf, proving detrimental to U.S. seafood and tourism industries.”
On average, the dead zone is roughly the size of the U.S. state of Connecticut.
The U.S. Geological Survey (USGS) reported discharge into the watershed to be about 29 percent above average in May 2025, leading NOAA scientists to calculate an average dead zone this summer.
“USGS measures river discharge and nutrient levels using approximately 3,007 real-time streamgages, 97 real-time nitrate sensors, and 37 long-term monitoring sites in rivers throughout the Mississippi-Atchafalaya watershed,” the National Ocean Service said. “These data are used to track long-term changes in nutrient inputs to the Gulf and to build models of nutrient sources and hotspots within the watershed.”
NOAA uses a suite of models developed with the University of Michigan, Louisiana State University, William & Mary’s Virginia Institute of Marine Science, North Carolina State University, and Dalhousie University to produce its forecast. The agency typically conducts a cruise later in the summer to measure the hypoxic area and confirm the size of the dead zone.
The dead zone ranges in size every year; last year’s dead zone was 6,705 square miles – the 12th largest zone recorded in nearly 40 years.
“Obviously, you don't like it to be bigger in the years when it's bigger, but then we also need to keep it in perspective in years when it's smaller. It's the trend over time that we're looking at,” Louisiana State University Coastal Research Scientist Doug Daigle told the Louisiana Illuiminator.
Federal and state groups are working to reduce the size and impact of the dead zone.
The Interagency Mississippi River and Gulf of America Hypoxia Task Force’s goal is to reduce the dead zone to 1,900 square miles by 2035 by reducing excess nutrient pollution into the watershed. However, the Trump administration’s cuts to the federal workforce and planned cuts to the budget – which target NOAA, the U.S. Environmental Protection Agency, and environmental spending more generally – could undermine those efforts through reduced funding and fewer staff resources to address the problem.
Earlier this year, lawmakers in Congress introduced legislation to reauthorize and strengthen the 1998 Harmful Algal Bloom and Hypoxia Research and Control Act (HABHRCA), which supports state and federal coordination in addressing algal blooms and hypoxia.
“The scale and frequency of harmful algal blooms and hypoxia events continue to increase with climate change, damaging beloved places, harming fisheries central to coastal economies, affecting tourism, and threatening public and ecosystem health,” U.S. Representative Suzanne Bonamici (D-Oregon) said in a statement. “This legislation will empower coastal and freshwater communities to better monitor these disastrous events and leverage research to mitigate and prevent their worst effects.”
The bill would direct the federal government to develop a comprehensive strategy to address algal blooms. It would also codify the National Harmful Algal Bloom Observing Network, integrating monitoring and forecasting efforts. If passed, the legislation would authorize USD 27.5 million (EUR 23.8 million) for HABHRCA activities and another USD 2 million (EUR 1.7 million) for the Harmful Algal Bloom or Hypoxia Event of National Significance program. The bill was approved by the Senate Committee on Commerce, Science, and Transportation in February 2025 but has not yet been taken up by the full Senate.
