Millions of Tons of Seaweed Could Soon Hit US

Millions of tons of seaweed could hit Florida shores by the summer holidays, according to scientists.

Record-breaking quantities of sargassum seaweed have already surged through the Caribbean and parts of the Atlantic, leaving beaches from Puerto Rico to Guyana blanketed in algae, said Live Science, citing a report by the University of South Florida’s (USF) Optical Oceanography Laboratory.

Authors of the USF study have been contacted via email for comment.

Why It Matters

The mounting sargassum bloom not only disrupts ecosystem balance but also threatens the economies of beach-reliant U.S. states such as Florida, where anticipatory cleanup costs can run into millions. Decaying sargassum poses health risks, emits noxious gases, and smothers marine habitats and tourist beaches alike, underscoring a cascading set of environmental and economic challenges well beyond the Caribbean islands.

With the current scientific consensus suggesting that sargassum levels typically peak in summer months, there is a strong likelihood that U.S. Gulf and southeast Atlantic beaches will see direct impacts—potentially affecting tourism, public health, and marine life for weeks or months.

What To Know

Scientists documented more than 37 million metric tons of sargassum in May 2025, shattering previous records set just two years earlier, said USF’s lab.

Researchers and regional officials expected the sargassum mass to continue growing and drifting, with the west Caribbean Sea and Gulf of Mexico—including Florida—now under threat of similar impacts through the coming weeks. Tourist hotspots in the region have already begun emergency response and monitoring efforts, according to NBC News.

Satellite observations by the USF found the latest mass had surpassed the previous 2022 record by more than 15 million tons. Professor Chuanmin Hu of USF, who monitors sargassum movement, said the “total amount has exceeded the previous all-time high” and warned the mass “will continue to grow” in the coming months, according to USA Today.

Why Sargassum Is Increasing

The underlying causes for the bloom remain unclear. Scientists are investigating factors including warming ocean temperatures, nutrient-rich runoff from agriculture, and changing wind and current patterns, but have not settled on a definitive explanation. “It’s the million-dollar question,” Brian Barnes, assistant research professor at USF and report co-author, told NBC News, adding, “I don’t have a supremely satisfying answer.”

Health and Environmental Risks

While floating sargassum supports marine life such as crabs and sea turtles, beached and decaying masses emit ammonia and hydrogen sulfide—a combination that can hamper breathing and force beach closures. Schools in Martinique and Anguilla closed temporarily this spring in response to strong odors, with similar risks to coastal communities in the US as seaweed arrives, said Live Science.

Wildlife is threatened, too. Large sargassum deposits can block sunlight needed by coral reefs and sea grass meadows, while organisms within the wash die or are scavenged by birds. Local cleanup operations risk further disturbance, particularly to nesting sea turtle habitats, said PBS NewsHour.

Caribbean island resorts and officials have declared states of emergency, investing in barriers, storage vessels, and extended cleanup work to limit the impact.

Forecast for US Shores

Scientists expect the sargassum mass will further expand into June and July along prevailing ocean currents, increasing the chances of significant seaweed arrivals on U.S. beaches—particularly across Florida’s Atlantic and Gulf coasts. The specific extent and locations depend on unpredictable currents and wind patterns, with annual peaks historically occurring in midsummer.

What People Are Saying

Outlook of 2025 Sargassum blooms paper for the University of South Florida: “As in most previous years, June is expected to see continued increases in most regions. More Sargassum is expected to be transported to the west Caribbean Sea and then to the Gulf through the Yucatan. Sargassum inundation will continue to occur in most of the Caribbean nations and islands as well as along the southeast coast of Florida.”

Barry Rosen, professor in the Department of Ecology and Environmental Studies at The Water School at Florida Gulf Coast University, told ABC News: “We have not seen catastrophic impacts that the Caribbean has seen, but this year could be different, and this is what we’re bracing for right now.”

What Happens Next

There is a significant amount of sargassum in the water, but whether it all washes upshore in Florida depends on currents and winds over the next few weeks and months.