1,332 square miles: the second smallest "dead zone" in the Gulf of Mexico in 40 years. This positive development is accidental. What hypoxia erases from the seabed- and why it matters to an underwater photographer.
A dead zone, or hypoxic zone, is an area of water where the concentration of dissolved oxygen is too low to support most marine life (below 2 mg/L). In the Gulf of Mexico, this zone forms each summer near the mouth of the Mississippi River, due to large amounts of nitrogen and phosphorus fertilizers that are drained from agricultural areas in the central United States. These nutrients trigger algal blooms, which consume available oxygen as they decompose in the water layer close to the seabed.
Why was the dead zone in the Gulf of Mexico small in 2026?
The hypoxic zone in 2026 (1,332 square miles, measured from July 24th to 30th aboard the R/V Pelican) is the second smallest since monitoring began in 1985. The cause was Tropical Storm Bertha, which crossed the northern Gulf of Mexico just before the research cruise's departure. This storm mixed the water column and brought oxygen from the surface layers down to the bottom. This is not a structural improvement- nutrient inputs from the Mississippi River basin remain at the same level.
Since when has the NOAA been measuring the dead zone in the Gulf of Mexico?
The annual monitoring of the hypoxic zone in the Gulf of Mexico began in 1985, providing over 40 years of continuous data. This is one of the longest time series available on coastal hypoxia worldwide. The 2026 expedition took place from July 24th to 30th aboard the research vessel *Pelican* (LUMCON), with funding and coordination provided by NOAA.
What does the seabed look like in a hypoxic zone?
In areas with severe hypoxia, fish will migrate to waters with better oxygen levels. Benthic organisms- such as worms, bivalves, echinoderms, and small crustaceans- that cannot move will die in place. The seabed becomes a decomposition environment devoid of predators or mobile prey. For an underwater photographer documenting benthic fauna, this is literally a zone of visual silence: nothing moves, and nothing lives in the way that a healthy seabed does.
Will hypoxia in the Gulf of Mexico improve over time?
Scientific projections are not optimistic. The influx of nutrients from the Mississippi River basin depends on agricultural practices across a vast territory. Climate change is also altering river flow rates, surface temperatures, and the frequency of mixing events like the one predicted for Bertha in 2026. The small size of the affected area this year is a meteorological anomaly- not an indication of a positive long-term trend.
Ink is a weekly series about recent marine discoveries. The ink of writing. The anchor of the seabed. Each issue features news and insights into how these discoveries impact underwater photography.
"It is strange that the sea, from which life first arose, is now threatened by the activities of only one form of that life." Rachel Carson, The Sea Around Us, 1951
On August 5, 2026, NOAA announced some good news.
The annual hypoxic zone in the Gulf of Mexico measured 1,332 square miles in 2026. This is the second smallest area recorded since monitoring began in 1985, representing over 40 years of continuous data. Headlines reported an unexpected result, a positive surprise, and relief for fisheries in the Gulf.
The good news is real. It is also entirely accidental.
A Zone of Silence on the Seabed
Each year since 1985, a team from Louisiana State University and the Louisiana Universities Marine Consortium (LUMCON) boards the R/V Pelican and measures dissolved oxygen in the waters of the Gulf of Mexico, between the mouth of the Mississippi River and the coast of Texas.
They are looking for the extent of the hypoxic zone: the area where the oxygen concentration falls below 2 mg/L, a level below which most marine organisms cannot survive.The formation of this area is mechanical and recurring. Every spring, runoff from the agricultural basin in the central United States - a territory of several million square kilometers largely cultivated with nitrogen and phosphorus fertilizers - flows into the Mississippi River and its tributaries, eventually reaching the Gulf. These nutrients fertilize the surface, causing algae to proliferate. When these algae die and decompose, bacteria consume the oxygen in the water layer near the bottom. Summer thermal stratification prevents mixing between the oxygen-rich surface waters and the oxygen-depleted bottom waters.
The result: every summer, an area of the Gulf floor becomes uninhabitable.
For fish and shrimp, this means a migration to areas with better oxygen levels. For benthic organisms - polychaete worms, bivalves, echinoderms, small crustaceans - that cannot move, it means death in place. For an underwater photographer documenting bottom fauna, this means something very specific: a zone of visual silence. Nothing moves, nothing lives as a healthy seabed would.
What Made the Difference in 2026 - and Why It's Concerning
The measurement cruise took place from July 24 to 30, 2026. The result: 1,332 square miles of hypoxic zone, the second smallest since the beginning of monitoring.The cause of this decrease is not an improvement in agricultural practices in the Mississippi River basin. It's also not a reduction in nutrient inputs, nor a change in land management policies. It's due to Tropical Storm Bertha.
Bertha crossed the northern part of the Gulf of Mexico just before the start of the measurement cruise. As it passed through, it mixed the water column, blending the oxygen-rich surface waters with the nutrient-depleted bottom waters, and temporarily neutralized the thermal stratification that allowed the hypoxic zone to persist.
This weather event, lasting only a few days, achieved what decades of discussions about agricultural nutrient management have failed to do sustainably.
What this reveals: The "good news" from 2026 doesn't reflect any fundamental change. Nutrient inputs from the Mississippi River basin remain at the same level as in 2024 or 2023. The storm's ability to temporarily "solve" the problem highlights just how much the normal solution – reducing nutrients at the source – remains unachieved.There is a parallel with what climate change is doing to coral bleaching: natural variability can sometimes produce local recoveries or temporary improvements, which mask the underlying trend. The early bleaching observed at Cheeca Rocks in July 2026 is the same logic reversed- a single thermal event that reveals systemic fragility.
And the slowing of the AMOC adds another layer- changes in major ocean circulation systems alter stratification patterns, surface temperatures, and the frequency of mixing events. What worked this year with Bertha will not work the same way in a Gulf with stronger thermal stratification.
Dead Zones and Underwater Photography
A hypoxic zone doesn't have any particular color when viewed from the surface, and it can't be seen from a boat. You could sail over it for hours without knowing that you are above 1,332 square miles of seabed where nothing complex lives.This is one of the reasons why these areas have taken time to enter the collective consciousness. They lack the dramatic visibility of an oil spill or a bleached reef. They are invisible from above.
From below, it's a different story.
A diver descending into the few meters accessible above a hypoxic zone observes a transition. The benthic fauna gradually disappears: sea urchins, starfish, sea cucumbers, and bivalves that normally inhabit a sandy coastal seabed. What underwater photography documents in these areas is an absence. A flat bottom, devoid of biological features, where the only visible activity is microbial.
This type of documentation has value precisely because it is difficult to obtain. An image of a hypoxic seabed is not spectacular in the classic sense. It doesn't produce "contest-winning" photos. But it documents a state that satellite data and surface measurements cannot reveal in the same way.The marine protected areas created in recent years generally do not cover coastal agricultural hypoxic zones, because these zones are defined by criteria related to the presence of remarkable biodiversity, rather than the temporary absence of all life. This is one limitation of the current protection system: it protects what is visible and identifiable, but less well what gradually disappears.
This is a practice that develops over time. It requires the ability to return to the same sites year after year and document the differences. This is one of the guiding principles of the AquaExposure underwater photography course: developing a practice that endures rather than focusing on isolated events. Complete information is available on the AquaExposure course.
Frequently Asked Questions
What is a dead zone in the ocean?A dead zone, or hypoxic zone, is an area of water where the concentration of dissolved oxygen is too low to support most marine life (below 2 mg/L). In the Gulf of Mexico, this zone forms each summer at the mouth of the Mississippi River, fueled by agricultural fertilizers drained from the central United States.
Why was the dead zone in the Gulf of Mexico small in 2026?
Tropical storm Bertha crossed the northern part of the Gulf just before the measurement cruise (July 24-30, R/V Pelican), mixing the water column and bringing oxygen up from the depths. The area measured 1,332 square miles: the second smallest in 40 years of monitoring. Nutrient inputs from the Mississippi have not decreased: this is a meteorological effect, not a structural improvement.
Since when has NOAA been measuring the dead zone in the Gulf of Mexico?
Since 1985, which represents over 40 years of continuous data. This is one of the longest time series on coastal hypoxia in the world.
What does the seabed look like in a hypoxic zone?
Fish migrate to areas with better oxygen levels. Benthic organisms that cannot move (worms, bivalves, echinoderms) die in place. For an underwater photographer, this is a zone of visual silence: a flat bottom with no complex biological activity.
Will hypoxia in the Gulf of Mexico improve over time?The projections are not optimistic. Nutrient inputs from the Mississippi River basin depend on practices across a vast territory. Climate change is also altering thermal stratification patterns and the frequency of mixing events. The small size in 2026 was a meteorological anomaly.
You can find previous issues of "L'Encre" on the AquaExposure blog. And for developing an underwater photography practice that considers the long term, comprehensive resources are available on the AquaExposure training platform.
1,332 square miles of uninhabitable seabed this summer in the Gulf of Mexico. The second smallest area recorded in 40 years. Good news- and a tropical storm to thank.
