NOAA-supported scientists announced today that this year’s Gulf “dead zone” — an area of low to no oxygen that can kill fish and marine life — is approximately 4,402 square miles, the 15th smallest zone on record in 39 years of measurement. This equates to more than 2.8 million acres of habitat potentially unavailable to fish and bottom-dwelling species.
Scientists at Louisiana State University and the Louisiana Universities Marine Consortium (LUMCON) led the annual dead zone survey July 20-25 aboard LUMCON research vessel Pelican. This annual measurement is a key metric that informs the collective efforts of the Mississippi River/Gulf of America Hypoxia Task Force, a state/federal partnership that has set a long-term goal of reducing the five-year average extent of the dead zone to fewer than 1,900 square miles by 2035.
While the NOAA-supported research surveys provide a one-time snapshot of the dead zone, the five-year average captures the zone’s changing nature over time. The five-year average size of the dead zone is now 4,755 square miles, more than two times larger than the 2035 target.
In June, NOAA predicted an average-sized dead zone of 5,574 square miles, based primarily on Mississippi River discharge and nutrient runoff data from the U.S. Geological Survey. The measured size fell within the uncertainty range for NOAA’s ensemble forecast, demonstrating the overall accuracy of the underlying models and value in guiding nutrient reduction strategies.
Excess nutrients from the Mississippi-Atchafalaya River Basin stimulate an overgrowth of algae in the Gulf of America. When these algae die and decompose, they deplete oxygen in the water as they sink to the bottom. The resulting low oxygen levels (hypoxia) cause animals, like fish and shrimp, to leave the area. Exposure to hypoxic waters has been found to alter fish diets, growth rates, reproduction, habitat use and availability of commercially harvested species such as shrimp.
In June 2022, the Environmental Protection Agency established the Gulf Hypoxia Program to accelerate nutrient reduction actions by the Hypoxia Task Force and advance its Gulf Hypoxia Action Plan. As a result, the Hypoxia Task Force states are scaling up their nutrient reduction strategies.
In addition to its annual hypoxia forecast and survey, NOAA supports efforts to improve monitoring technologies and study hypoxia’s impacts on fish and fisheries in the Gulf of America and elsewhere through its Coastal Hypoxia Research, Ocean Technology Transition, Uncrewed Systems and Hypoxia Watch programs. NOAA also partners with states to develop new tools to predict nutrient runoff to waterways and supports the Northern Gulf Institute in delivering technical assistance, observation and monitoring capabilities.
NOAA scientists and partners are continuing to investigate the feasibility of using autonomous surface vehicles (ASVs) as an emerging technology to map hypoxia in the Gulf of America. This year, several ASVs were deployed in coordination with the measurement survey, which will be compared with the ship-based measurements.
This work is authorized under the Harmful Algal Bloom and Hypoxia Research and Control Act (33 U.S.C. §§ 4001 et seq.).