The seaweed itself is not harmful to humans, but decaying sargassum on beaches releases hydrogen sulfide that can impact people with breathing issues. That said, even decaying sargassum is not considered harmful because the gases disperse quickly on breezy beaches.

In 2026, sargassum (brown seaweed) remains a significant seasonal concern for the Florida Keys, particularly during the warmer months from March through July. While the Keys are famous for their turquoise waters, their location in the path of the Florida Current makes them a primary landing spot for the "Great Atlantic Sargassum Belt." Large mats of the seaweed can wash ashore, where they decompose and release hydrogen sulfide gas, which has a distinct "rotten egg" smell and can irritate those with respiratory issues. The severity is "patchy"; because the Keys have a complex coastline with many "dead-end" canals and shallow bays, the seaweed can become trapped in certain areas (like the Atlantic-facing beaches of Islamorada or Key West) while other spots remain perfectly clear. Most high-end resorts in the Keys now employ "beach grooming" teams to remove the weed daily, and many boat captains adjust their snorkeling locations to the "leeward" side of the islands to find clear water. Travelers in 2026 are encouraged to check "seaweed forecasts" and local beach cams, as a beach that is covered in sargassum on Monday can be completely clear by Wednesday if the winds and currents shift.