How Brown Sargassum Seaweed Could Affect Your Beach Vacation

Seaweed that’s part of what is known as the Great Atlantic Sargassum Belt is once again washing ashore and making headlines that might leave beachgoers wondering if their upcoming sand-filled getaways in the Caribbean, Mexico, and Florida might be plagued with a layer of rotting, stinking algae.

Record-breaking amounts of sargassum in the eastern Caribbean and Western Atlantic were reported in July by the University of South Florida’s Optical Oceanography Lab.

The unwanted seaweed washing ashore has been plaguing beaches in recent months everywhere from Puerto Rico and the Dominican Republic to the French Caribbean, Florida’s Atlantic coast, Mexico, and even shorelines in Brazil, where the seaweed’s sheer density caused fishing nets full of the stuff to capsize fishing boats.

“Unlike most previous years, total sargassum amount in the entire Atlantic Ocean (including the Caribbean Sea and Gulf of America) increased slightly to 38 million metric tons in July,” the July report stated, adding that, historically, sargassum amounts have mostly decreased from July to August.

The report attributes that growth to “the substantial increases in 3 of the 5 regions, namely the Gulf of America, western Caribbean, and eastern Caribbean, mostly due to physical transport of sargassum.”

It goes on to say that significant sargassum inundation events have “continuously been reported around most Caribbean nations and islands, including the Mexican Caribbean coast,” with small amounts of the seaweed reaching the Straits of Florida and “mild beaching events” along Florida’s southeastern coast.

To better understand what the seaweed influx means for some of our favorite beach destinations right now, we reached out to some experts.

What is sargassum?

Chances are if you’ve ever been on a beach lapped by the Atlantic Ocean or Gulf of Mexico, you’ve already encountered sargassum, in whatever small amount, along the shoreline or in the water.

The naturally occurring brown seaweed floats freely on the ocean’s surface, extending as deep as 10 feet below the surface, and sometimes makes its way to shore with currents and wind.

“It’s a floating brown macroalgae, related to kelp, but it’s always afloat, never attached to the bottom,” explains Brian Barnes, an expert on marine sciences and assistant professor at the University of South Florida, which collects data on sargassum blooms in the Caribbean Sea.

Sargassum is composed of gas-filled structures that look like berries called pneumatocysts that keep it buoyant.

Visible from outer space, the Great Atlantic Sargassum Belt that’s currently making headlines stretches 5,000 miles long and 300 miles wide in an area of the Atlantic Ocean between the Gulf of Mexico and the coast of West Africa. Right now, says Barnes, it measures a whopping 38 million metric tons. Prior to 2025, the record was roughly 22 million metric tons in June 2022, he says.

“It’s a good thing when it’s out offshore,” says Brian LaPointe, a research professor with Florida Atlantic University Harbor Branch Oceanographic Institute in Fort Pierce, Florida about the seaweed.

“Sargassum provides habitat for hundreds of species and invertebrates and even endangered sea turtles, supporting pelagic fisheries like mahi mahi and other fish that feed on prey items.” (Pelagic fish are fish that live and eat near the water’s surface.)

“It’s when it comes ashore in mass, that’s when it becomes a problem,” LaPointe says.

Which beaches and destinations are most affected by the growing sargassum belt?

It’s important to remember that where sargassum accumulates is highly variable. “It can come in one day with strong winds and pile up, and the next day the wind may shift and currents can change and will carry this stuff offshore,” LaPointe says.

Winds, currents, and tides all interact to make it very complex to predict where the sargassum is most likely to land during any given day, week, or month. “Mexico, the Riviera Maya area, has seen record amounts—more than they’ve ever seen this year,” LaPointe says, adding that Puerto Rico and the eastern Caribbean, including the French Antilles, have also been heavily impacted in recent months.

“This is not the first time we’ve seen major blooms,” Barnes says, pointing to record blooms in 2018 and 2022. However, there were no such major blooms prior to 2011, he adds, saying there is no clear explanation for why.

Travelers headed to destinations where they worry sargassum could be impacting beaches might want to consider doing some research ahead of time by inquiring with people on the ground to know what to expect.

LaPointe says to keep in mind that there are a lot of areas that haven’t been impacted this year, and that autumn usually brings some respite. By mid- to late summer, he says, nutrient supply discharged by rivers starts to decrease. “In the fall, typically, the [sargassum belt] biomass decreases as its growth decreases with decreasing nutrient supply,” he says, with much of it decomposing on beaches or falling to the bottom of the ocean.

“We should begin to see the sargassum decreasing . . . and then by winter, January and February, we’ll start to see that seasonal growth cycle begin again,” he says.

Is there anything destinations and beachfront hotels and resorts can do to mitigate the problem?

Keeping sargassum at bay from a beach where it’s determined to wash ashore is like fighting a rising tide. And scenes of workers pitchforking and shoveling piles of seaweed into waiting wheelbarrows around the clock have, unfortunately, become a somewhat standard oceanfront backdrop in recent years at beaches in popular warm-weather destinations like Playa del Carmen and Tulum in Mexico and Barbados in the Caribbean.

Apart from removing what washes ashore as it arrives, Barnes says a hotel might consider installing a floating boom offshore (usually made of PVC and deployed parallel to the shoreline) with the goal of preventing sargassum from coming ashore. But again, it represents a small measure against a monumental task.

Booms are not 100 percent effective, he says, and can only be implemented in relatively small areas in the context of the larger bloom. Because booms can’t be infinitely long, sargassum can seep in at their ends and still make its way to the sand. “Boom tech is getting better, but still can get overrun with sargassum,” Barnes says.

However, one place that’s likely to be perfect on a sunny day no matter what the Great Atlantic Sargassum Belt and ocean currents and winds are doing? That’s your hotel pool, preferably one with ocean views. After all, it never hurts to have a beach day backup plan.

Can you swim in the water when there is sargassum present?

Depending on how thick it is, swimming in water where sargassum is present may require pushing it out of the way to clear a route. And sargassum can feel scratchy, kind of like a loofah sponge, when it rubs up against you. (Dolphins have been reported to play with sargassum and may even use it to scratch themselves, according to the Wild Dolphin Project.)

But for humans, there can be some unpleasant conditions associated with swimming where sargassum is abundant, says LaPointe.

“You can swim in the water if there’s sargassum and people do, but I have seen some reports of sea lice associated with sargassum in water with big mats of it floating around,” he says, referring to small jellyfish larvae, which can cause the skin to erupt in a red, itchy rash.

“There are some risks of stinging organisms to be aware of,” LaPointe adds, referring to jellyfish that can also often be present among sargassum.

The odor of sargassum—which can smell like rotten eggs when it decomposes due to the production of the hydrogen sulfide gas—can be off-putting. LaPointe notes that there have been reports of respiratory issues in areas with large amounts of decomposing sargassum on the shore due to the hydrogen sulfide released.

Why is there so much sargassum right now?

As for what’s causing this year’s record sargassum bloom, Barnes says his lab has “a few hypotheses, but no solid answers,” adding that sargassum will bloom wherever the conditions—including variables like temperature, nutrients, and light—favor it.

“This year, temperatures during the growing season were a bit warmer than in previous years—but not too hot—while stronger winds have brought nutrient-rich deep water to the surface, which may have contributed to the accelerated growth,” he wrote to Afar in an email.

LaPointe points to extreme nutrient-loading earlier this year into the Amazon Basin watershed, off the east coast of South America, that began during extreme flooding in February as a potential culprit.

“When those floods hit, you get peak nutrient concentrations coming out with the flood waters in the bloom,” he says, adding that the Great Atlantic Sargassum Belt would have encountered the blast of nutrients in the western tropical Atlantic as it grew and moved from east to west.

Satellite imagery this year, examined month by month, confirms how the biomass exploded in this area, he explains. “It was just growing like crazy, like Miracle Grow,” says LaPointe.

“Just like land plants, you need the right light environment, the right temperature,” for growth, Barnes says, as well as a seed—the seed in this case is the population of sargassum that’s already out in the Great Atlantic Sargassum Belt.

Nutrients rising from the ocean depths or from rivers flowing into the region act as fertilizers, adding to the ideal conditions for growth. LaPointe says the scale of the current bloom is “all about the nutrients.”

“The more you feed it, the bigger it gets,” he says, adding that there’s evidence that nutrient runoff in the form of nitrogen and phosphorus from human activities and sources such as fertilizers, wastewater, automobile exhaust, and animal waste from rivers—including the Mississippi River, Amazon River, and Congo River—are feeding sargassum blooms all along the Atlantic Basin.

This story was originally published in March 2023, and was updated on August 15, 2025, to include current information.