A giant belt of sargassum stretches across the Atlantic: 37.5 million tons of brown algae

In the Atlantic Ocean a gigantic belt of floating brown algae sargassum, stretching from the coast of West Africa to the Caribbean and the Gulf of Mexico.

According to satellite data, in May 2025 its biomass reached a record 37.5 million tons. This is not a “new wall” that has appeared overnight, but is part of an expanding system known as the Great Atlantic Sargassum Belt, which has been observed regularly since 2011. The data is confirmed EUMETSAT and satellite monitoring from the University of South Florida.

It is important to clarify the date: the figure of 37.5 million tons refers to May 2025and not by this May 2026. At the same time, the current season is also considered potentially record-breaking: already at the beginning of 2026, researchers recorded unusually large volumes of sargassum in the Atlantic and Caribbean. According to experts, the volume of algae in 2026 may exceed last year’s maximum. Florida State University reports that by February 2026 there were more than 13 million tons of sargassum in the Atlantic.

What is Sargassum

Sargassum is a genus of brown algae, much of which floats freely in the sea and is not attached to the bottom. In the open ocean, such accumulations are not at all “natural trash”: they serve as shelter and food supply for fish, sea turtles, crabs and other organisms.

The problem begins when huge masses of algae wash up on the shore. On beaches they quickly decompose and emit an unpleasant odor and hydrogen sulfide. It can irritate the airways, especially in people with asthma and other chronic conditions. Warns of risks to health and coastal environment NOAA.

Beaches, tourism and fishing

https://www.youtube.com/watch?v=nSTujoYss78

For the Caribbean islands, Mexico, Florida and several Central American countries, sargassum has become a seasonal, national problem. Beaches have to be cleaned with heavy equipment, but mechanical cleaning can damage sand, turtle nests and coastal vegetation.

Massive releases of algae deteriorate water quality, create oxygen deficiency in coastal areas and interfere with fishing. For tourist regions, this is also a direct economic blow: hotels and municipalities spend large sums on cleaning the coast, and vacationers are not too willing to pay for a view of the sea, which resembles a swamp soup with the smell of sewage.

Why is the belt growing?

Scientists attribute the expansion of the Great Atlantic Sargassum Belt to a combination of natural and man-made factors. Among them are ocean currents, changes in winds, water temperature and the supply of nutrients, especially nitrogen and phosphorus.

Agricultural runoff, deforestation, urban wastewater, and river runoff, including from the Amazon, may all play a significant role. The water receives additional “feeding”, and the algae use it with alarming efficiency. A study on the mechanisms of belt formation was published in Scienceand more recent work from 2026 shows that the influence of land-based nutrient sources is becoming more pronounced. Nature Communications

The problem is not only for tourists

Sargassum in the open ocean remains an important part of the marine ecosystem. Therefore, the task is not limited to “remove all the algae.” Scientists warn that uncontrolled collection at sea could harm the species that depend on the floating bushes for habitat.

The big question is how to reduce the flow of nutrients into the ocean and how to protect coastlines from massive algal blooms without destroying coastal ecosystems. For the Caribbean countries, this is no longer an exotic environmental issue, but a matter of health, tourism, fisheries and local budget expenditures.

Sources: EUMETSAT, EPA, NOAA, Science, Nature Communications.

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