You can expect a “major” year for seaweed, raising the chances that more will wash up on Florida beaches in 2025, experts say.
Researchers at the University of South Florida used satellite imagery to determine monthly amounts of sargassum in the Atlantic Basin, and found that December had exceptional amounts of the seaweed.
The ongoing research showed that sagrassum amounts in the Gulf of Mexico, western Caribbean Sea, and eastern Caribbean are currently low, which is normal for this time of year.
But that was not the case in the Atlantic Ocean. The western Atlantic had a significant increase in sargassum from November as a result of both local blooms and seaweed traveling west from the waters off Africa.
The band of seaweed annually stretches across the Atlantic, peaking in summer, and drifts west, often piling up on islands in the Caribbean, or continuing into the Gulf of Mexico. From there, much of it rounds Florida and ends up clumping (and smelling) on east coach beaches.
The study found that when compared to previous Decembers since 2011, sargassum amounts exceeded each region’s 75th percentile, meaning they were well above average, and close to maximum.
The report said that during the last week of December, small amounts of sargassum had already reached the Lesser Antilles.
Sargassum growth normally increases from January onward, and it will continue to drift westward, toward the U.S., and though there’s not much in our region just yet, that is likely to change: “Because of the relatively high amounts of Sargassum in the tropical Atlantic,” the report said, “2025 is likely another major Sargassum year.”

Sargassum amounts have spiked in the last 15 years, bringing frustration to South Florida beachgoers and causing substantial economic damage in the Caribbean.
Though it supports marine life in the open ocean, once it decomposes on shore, it can release hydrogen sulfide, a gas that has an odor reminiscent of rotten eggs, and can cause respiratory problems.
The reason for the spike seems to be a phenomenon known as the Great Atlantic Sargassum Belt (GASB), a massive, sometimes 5,000-mile-wide bloom of sargassum that did not exist until 2011.
The belt forms closer to the equator than where sargassum historically formed, farther north on the Atlantic.
A 2023 study by Woods Hole Oceanographic Institute, Florida Atlantic University and others links the larger blooms to higher concentrations of nutrients in Atlantic waters near the equator, compared to those farther north in the Sargasso Sea, where the macroalgae historically grew.
Finding higher nutrients in the Great Atlantic Sargassum Belt “is a smoking gun that the GASB inundations are nutrient-driven,” said Dennis McGillicuddy, of Woods Hole, lead author of the study.
his story was produced in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative founded by the Miami Herald, the South Florida Sun Sentinel, The Palm Beach Post, the Orlando Sentinel, WLRN Public Media and the Tampa Bay Times.