Stink-free beaches: Masses of seaweed likely won’t reach Florida until May, researchers say

It looks as though Florida won’t see much — if any — stinky seaweed washing up on its beaches until late April or May, according to the University of South Florida’s monthly sargassum report.

That’s a relatively late start for the algal blooms to pile up on our shores, though sargassum in Florida usually peaks in July.

Holding your nose and hopping over piles of dead sargassum while visiting South Florida beaches has become much more common since 2011, when the algal blooms out in the Atlantic shifted south, closer to the equator, where they found warm water and nutrients.

The spike has been dubbed the Great Atlantic Sargassum Belt, a massive, sometimes 5,000-mile-wide bloom that has begun to form near the equator each spring and drift our way.

The spike has brought frustration to South Florida beachgoers and caused significant economic damage to resort areas in the Caribbean and Yucatan.

USF’s report, which analyzes satellite data, found that though February 2024 had very high levels of sargassum off Africa compared to the past dozen years, other regions, especially those adjacent to Florida — the Eastern and Western Caribbean Sea and the Gulf of Mexico — had lower than normal sargassum levels.

As a result, Florida should be relatively sargassum-free until late April or even May.

Though sargassum mats support a resplendent array of marine life as they drift out at sea, once they decompose on shore, they can release hydrogen sulfide, a gas that has an odor reminiscent of rotten eggs, and can cause respiratory problems.

In 2022, massive clumps of sargassum obstructed the water intake of a desalination plant on St. Croix, in the U.S. Virgin Islands, leaving the plant barely able to provide enough fresh water for the island, prompting officials to declare a state of emergency.

A study last summer linked the sargassum belt 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.

The southernmost swath of the belt, along Brazil and Venezuela coast, had the highest levels of nutrients, and also lower salinity, indicating that it is “under the direct influence of the Amazon River plume … which has been implicated as a nutrient source for the GASB.” The study says the Congo River is another potential source.

Bill Kearney covers the environment, the outdoors and tropical weather. He can be reached at bkearney@sunsentinel.com. Follow him on Instagram @billkearney or on X @billkearney6.