Tourists hoping to spend a day on the beach in Playa del Carmen, a popular coastal resort town near Cancun, Mexico, were disappointed to find the sand almost completely covered in large amounts of seaweed.
A video captured by Instagram user Ahianvlog on May 30, later going viral on TikTok thanks to Accuweather, showed a beach covered in sargassum seaweed, a type of brown seaweed that often accumulates in large masses in the Atlantic Ocean.
What is sargassum?
Sargassum seaweed forms large brown clumps and is carried by currents and wind. A 2019 study found that sargassum seaweed often forms off the west coast of Africa in the so-called Great Atlantic Sargassum Belt.
Climate change has also been found to affect the growth of ocean algae, as fluctuations in sea level, water temperature, water acidity, and other factors impact algae development.
File photo: Harvesting sargassum seaweed on the beach in Bavaro, Punta Cana, 2018.
Cause for concern
Sargassum seaweed may seem like a harmless (if somewhat off-putting) beach phenomenon, but experts say it may be a cause for concern.
A new study published in March 2026 took a closer look at arsenic levels in Sargassum seaweed and how it affects children, especially those on the beach.
Sargassum seaweed, as part of the groundwater cycle, naturally accumulates large amounts of arsenic as water moves from groundwater into reservoirs and then into the ocean.
Sargassum seaweed
When sargassum seaweed washes ashore, it begins to decompose, which prevents it from retaining arsenic.
The risk increases with skin contact and ingestion.
«Given the data we have, the risks are low,» she said. Newsweek In an email, Helen Solo-Gabriele, a professor in the University of Miami's School of Engineering and the study's author, said:.
«"However, there are gaps in our knowledge. Research is needed to improve our understanding of the risks.".
Solo-Gabriele added that basic hygiene is important, recommending washing hands and showering after visiting the beach, as well as avoiding "games that can significantly increase the risk of infection, such as burying yourself in the sand.".
Warning smell
The decomposition of the algae also produces a sulfur-smelling gas, which the researchers say is "only part of the problem.".
«"As sargassum seaweed decomposes, it can release hydrogen sulfide and other sulfur-containing gases, and these emissions can pose a hazard when sargassum seaweed accumulates in large piles," study co-author Jiayu Li said in a press release.
«"If beachgoers experience a strong rotten egg odor or irritation to the eyes, throat, or respiratory tract, it is a good sign to leave the area.".
Solo-Gabriele said the amount of sargassum seaweed washing ashore in the Caribbean and Florida is expected to increase due to ocean circulation.
«"We need to conduct further research to predict the transport of Sargassum seaweed from the ocean to its beaching sites, and to predict the potential public health impacts of beaching seaweed," she said.
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