Seaweed, part of what is known as the Great Atlantic Salgassum Belt, is again washing on land, and may make headlines that may make you wonder if the upcoming sand-filled holidays in the Caribbean, Mexico and Florida are rotten.
Record volumes of Sargassum in the Eastern Caribbean and Western Atlantic were reported in July by the University of South Florida’s Optical Oceanography Laboratory.
Unwanted seaweed washing land has plagued beaches everywhere, from Puerto Rico and the Dominican Republic to the French Caribbean Sea, to Florida’s Atlantic Coast, Mexico and even Brazilian coastlines, where the pure density of seaweed caused fishing nets filled with fishing boats.
“Unlike most years in the past, the total amount of Sargassum across the Atlantic (including the Caribbean and the Gulf of America) increased to just 38 million tonnes in July,” the July report added that historically, Sargassum volumes have declined primarily between July and August.
The report attributes growth to a significant increase in the US Gulf, the Western Caribbean and the East Caribbean.
Additionally, Sargassum flooding events are being reported continuously around most Caribbean countries and islands, including Mexico’s Caribbean coast.”
Now, we have contacted some experts to better understand what seaweed influx means for our favorite beach destinations.
What is Sargassum?
If you’ve ever been to a beach wrapped in the Atlantic or Gulf of Mexico, you could have encountered any amount of Salgassum along the coastline and underwater.
Naturally occurring brown seaweed floats freely on the surface of the ocean, stretching deep 10 feet below the surface, sometimes heading towards the shore with currents and winds.
“A floating brown macroalgae associated with kelp, but they are always floating and never at the bottom,” explains Brian Burns, a marine science expert at the University of South Florida, who collects data on Salgassum Bloom in the Caribbean.
Sargassum is made up of a structure filled with fruit-like gases called bronchial cysts.
The Atlantic Salgassum belt, which is currently making headlines, is a region of the Atlantic Ocean between the Gulf of Mexico and the coast of West Africa, extends to 5,000 miles long and 300 miles wide. Now, Burns says, it measures a whopping 38 million tonnes. Before 2025, the record for June 2022 was around 22 million tons, he says.
“When you’re out offshore, that’s good,” says Brian Rapoient, a research professor at the Harbour Branch Marine Research Institute at Florida Atlantic University in Fort Pierce, Florida, about seaweed.
“Sargassum provides habitat for hundreds of species, invertebrates, and even endangered sea turtles, supporting feathery fisheries like mafia and other fish and feeding on prey.” (Peragic fish are fish that live and eat near the surface.)
“That’s when there’s a lot of landfall, when it’s a problem,” says Lapointe.
Which beaches and destinations are most affected by the growing Salgassumbelt?
It is important to remember that the accumulation of Sargassum is very diverse. “It’s going to be strong winds and piles one day. The next day, the wind changes, the flow changes, and sometimes things like this can be carried off the coast,” says Lapointe.
The wind, flow, tides, and tides all interact to make them extremely complicated to predict where Sargassum is most likely to land on a particular day, week or month. “Mexico, the Riviera Mayan region, has seen a record amount than we’ve seen this year,” Lapointe said, adding that Puerto Rico and the Eastern Caribbean, including France’s Antilles, has also been heavily affected in recent months.
“This is not the first time I’ve seen a large flower,” Burns says. It refers to recording records in 2018 and 2022. However, before 2011 there were no such large flowers.
Travelers headed to their destination where they worried that Sargassum might be affecting the beach.
Keep in mind that Lapointe has many areas not affected this year, and that autumn usually provides some rest. He says that between summer and late summer, the nutrient supply discharged by the river begins to decrease. “In autumn, the biomass (Sargassum belt) usually decreases as growth decreases with reduced nutritional supply,” he says.
“We should start to see Sargassum dropping, and by winter, January and February, we will start to see the seasonal growth cycle begin again,” he says.
Are there any destinations or beachfront hotels or resorts you can do to alleviate the problem?
Keep Sargassum at bay from the beach. There, the beaches that are determined to wash are like fighting rising tides. And the worker scene was shoveling mountains of seaweed in a handcart waiting around the clock, and unfortunately, in recent years it has become a somewhat standard oceanfront backdrop at popular warm weather destinations such as Playa del Carmen and Tulum in Mexico, as well as popular warm weather destinations such as Barbados in the Caribbean.
Apart from removing anything to be washed on arrival, Burns says the hotel may consider installing a floating boom offshore (usually made of PVC and deployed parallel to the coastline) with the goal of preventing Salgassum from coming to land. But again, it represents a small measure of monumental work.
The boom is 100% ineffective, he says, and can only be implemented in relatively small areas in the context of larger florals. The boom cannot be infinitely long, so Sargassum penetrates its edges and can still reach the sand. “Boom Tech is getting better, but it still could overrun with Sargassum,” says Barnes.
But no matter what the Atlantic Sargassum belts, currents and winds are doing, what is one of the places that could be perfect on a sunny day? That’s your hotel pool and, if possible, have ocean views. After all, having a Beach Day backup plan is never a pain.
When Sargassum is present, can you swim in the water?
Depending on the thickness, you should avoid getting in the way to clean up the route by swimming in the water where Sargassum is present. And Sargassum can feel like some sort of rufa sponge, scratching it when rubbed against you. (Dolphins have been reported to play with Sargassum, and according to the Wild Dolphin Project, they can even use it to hurt themselves.)
However, for humans, there may be some unpleasant conditions associated with swimming, which is rich in Sargassum, Lapointe says.
“If you have Sargassum and people, you can swim in the water, but I’ve seen reports of sea lice related to Sargassum underwater with large mats floating around,” he says.
“There are some stinging creature risks to notice,” Lapointe adds, referring to jellyfish that can often be present among Sargassum.
Sargassum’s odor can smell like rotten eggs when decomposed for the production of hydrogen sulfide gas, but it can be unpleasant. Lapointe points out that there have been reports of respiratory problems in areas where there are massive amounts of decomposed Sargassum on the coast due to released hydrogen sulfide.
Why are there so many sargasams now?
As for the cause of this year’s record-breaking Sargassum Bloom, Barnes says his lab “There are a few hypotheses, but there is no solid answer.” Sargassum adds that it blooms anywhere with conditions that include variables such as temperature, nutrients, and light.
“This year, the temperatures during the growing season were a little warmer than in the past few years, but not too hot, but the strong winds have brought deep, nutritious water to the surface.
Lapointe pointed to extreme nutritional loads in the Amazon Basin basin off the east coast of South America earlier this year, beginning with extreme floods as a potential perpetrator in February.
“When these floods hit, they produce flowering floods and peak nutrient concentrations,” he says, adding that the Great Atlantic Salgassum Belt encountered a nutrient explosion in the tropical Atlantic Ocean in the western part of the tropical Atlantic, moving from east to west.
Satellite images examined monthly this year will see how biomass exploded in this area, he explains. “Like the growth of miracles, it was just growing like crazy,” says Lapointe.
“Like land plants, you need the right lighting environment and the right temperature,” Burns says. In this case, the seeds are already the population of Sargassum in the Atlantic Ocean’s Sargassum belt.
Nutrients rising from ocean depths and rivers flowing into the region serve as fertilizers and add to the ideal conditions for growth. Lapointe says the current scale of flowers is “about all nutrients.”
“The more you feed it, the bigger it will,” he said, adding that there is evidence of nutrients in the form of nitrogen and phosphorus from human activities such as fertilizer, wastewater, car exhaust, animal waste from rivers and sources.
This story was originally published in March 2023 and updated on August 15, 2025, and contains current information.
