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Massive amounts of sargassum, a brown seaweed that naturally floats in the Atlantic Ocean, are already washing ashore across South Florida, the Florida Keys and parts of the Caribbean—and researchers warn that the worst may still be ahead. According to the University of South Florida's Optical Oceanography Lab, 2026 will be "another major Sargassum year" and could even become a record-breaking one by the end of the summer. Major beaching events have already been reported along Florida's southeast coast, with more expected in the coming weeks.
For beachgoers, the biggest giveaway is the smell.
As sargassum piles up on shore and begins to decompose, it releases hydrogen sulfide gas, giving off the unmistakable odor of rotten eggs. "Beaching events around the Caribbean and southeast coast of Florida will continue and likely increase," the USF team wrote in its latest outlook.
The seaweed itself isn't dangerous, but Florida health officials say the tiny creatures that live inside the piles can sometimes cause skin irritation, rashes and blisters. The hydrogen sulfide released during decomposition can also irritate the eyes, nose and throat, particularly for people with asthma or other respiratory conditions.
That doesn't mean you need to cancel your beach trip, though. Officials recommend avoiding direct contact with large accumulations of seaweed, steering clear of swimming through thick patches and limiting time near heavy buildups if the odor causes irritation. (In open-air environments, like the beach, hydrogen sulfide concentrations generally don’t reach harmful levels.)
The phenomenon is tied to the Great Atlantic Sargassum Belt, a sprawling mass of seaweed stretching thousands of miles across the tropical Atlantic. Scientists say the belt has grown dramatically since 2011 and now regularly sends waves of seaweed into the Caribbean, Gulf Coast and Florida beaches each year. Sargassum season typically runs from March through October, with the largest accumulations coming during late spring and summer.
As unpleasant as it can be for your Instagram stories, sargassum isn't entirely the villain of the story. The seaweed provides shelter for fish, crabs, shrimp and sea turtles, helps nourish beaches and can even aid shoreline resilience after storms. In fact, environmental regulations generally prohibit removing it from the water before it reaches shore because of its ecological importance.
Still, if you've been dreaming of turquoise water and powdery white sand, be prepared for a less glamorous reality this summer. In some parts of Florida, beach days may come with an extra accessory: a faint whiff of rotten eggs riding in on the ocean breeze.