Caribbean Faces Growing Sargassum Crisis as Record Seaweed Blooms Threaten Beaches, Marine Life and Tourism

FREDERIKSTED, St. Croix — An enormous buildup of floating brown seaweed across the Caribbean has raised growing concerns about the region's coastal environment, marine ecosystems and tourism industry, following an exceptionally active sargassum season in 2026.

From Puerto Rico and the U.S. Virgin Islands to the eastern Caribbean and Mexico, large accumulations of sargassum have affected coastlines, creating challenges for residents, beach operators, fishermen and tourism-dependent businesses.

Scientists say the 2026 season was particularly significant, with record concentrations reported across portions of the Caribbean and Atlantic earlier this year.

According to the University of South Florida's Optical Oceanography Laboratory, approximately 34 million metric tons of sargassum were recorded across the Atlantic, Caribbean and Gulf region in June. By July, approximately 27 million metric tons remained.

The unprecedented concentrations prompted renewed concerns about the growing frequency and severity of these blooms.

A welcome decline, but the problem remains

There is, however, some encouraging news as the region approaches the winter tourism season.

Researchers expect the seasonal decline to continue through November and possibly December.

For Puerto Rico and the U.S. Virgin Islands, scientists say the immediate threat of major coastal inundation has diminished considerably.

Although smaller beaching events may continue, their expected severity is significantly lower than during the summer months.

Despite the improvement, researchers caution that sargassum levels remain historically elevated for this time of year.

Virgin Islands experienced significant impacts

The U.S. Virgin Islands were among the areas affected during the 2026 season.

In an earlier public advisory, the Virgin Islands Department of Planning and Natural Resources warned that shorelines throughout the territory could experience significantly elevated sargassum levels.

The warning was based on satellite observations and research conducted by the University of South Florida in collaboration with DPNR and regional partners.

During the height of the season, environmental consultant Amy Dempsey described the situation in the Virgin Islands as the worst she had witnessed in five years.

Some coastal areas experienced substantial accumulations, affecting access to the water and creating unpleasant conditions along shorelines.

Puerto Rico also experienced significant concentrations, including around popular coastal destinations such as La Parguera.

Environmental and public health concerns

While floating sargassum in open waters provides important habitat for fish, turtles and other marine organisms, excessive accumulations near shore can create serious environmental problems.

When large quantities wash ashore and begin decomposing, they release hydrogen sulfide and ammonia, producing a strong rotten-egg odor. Exposure to these gases can cause headaches, nausea and respiratory irritation, particularly among individuals with existing respiratory sensitivities.

Large accumulations in coastal waters can also reduce oxygen levels, affect mangrove ecosystems, smother seagrass beds and prevent sunlight from reaching coral reefs.

For coastal communities, the consequences extend beyond environmental concerns.

Beachfront businesses, hotels, restaurants, fishermen and tourism operators can experience significant economic losses when beaches become covered with decomposing seaweed.

What is causing the massive blooms?

Scientists have identified several possible contributing factors, including agricultural runoff, warming ocean temperatures, changing ocean currents, wind patterns and rainfall.

The recurring phenomenon now known as the Great Atlantic Sargassum Belt expanded significantly in 2011, establishing a pattern of large-scale blooms stretching from waters near West Africa toward the Caribbean and Gulf of Mexico.

Researchers have also observed unusual local growth in portions of the Caribbean and Gulf, raising additional questions about the factors driving the phenomenon.

However, scientists have not established a clear relationship between the blooms and larger climate patterns such as El Niño and La Niña.

Could the Caribbean face another major season in 2027?

While researchers anticipate continued reductions in sargassum concentrations through the end of 2026, questions remain about what the next season could bring.

The University of South Florida says it is monitoring changing conditions and expects to gain a clearer understanding of when concentrations may begin increasing again.

For now, environmental officials and researchers continue monitoring satellite imagery and issuing regional outlooks to help communities prepare.

The sargassum problem is no longer viewed as an occasional inconvenience for Caribbean islands. It has become a recurring environmental challenge with implications for public health, marine ecosystems and the economic stability of communities that depend heavily on their coastlines.

For the U.S. Virgin Islands and Puerto Rico, the recent decline offers some relief. However, the experience of 2026 serves as a reminder that the region must continue developing strategies to monitor, manage and respond to increasingly significant seaweed.