If you've noticed more seaweed washing ashore on Florida's Gulf and Atlantic beaches lately, there's a big-picture reason behind it. The Great Atlantic Sargassum Belt — a massive stretch of floating brown algae spanning the tropical Atlantic — reached its second-highest level ever recorded in June 2026, surpassed only by 2025, according to researchers at the University of South Florida College of Marine Science.
The numbers are striking. The Gulf of America logged 5 million metric tons of sargassum in June, nearly double its previous all-time high set just last year. The Caribbean fared no better: the western Caribbean registered 3.6 million metric tons and the eastern Caribbean hit 9 million metric tons — both record highs for those regions.
Scientists have been tracking a significant shift in sargassum behavior since 2011. The algae has been thinning in its historical home, the North Atlantic's Sargasso Sea, while spreading aggressively through the tropical Atlantic. That decades-long trend shows no sign of reversing, with satellite data confirming 2026 as another exceptional year.
The monitoring relies on NASA satellites, including the MODIS instruments aboard the Aqua and Terra spacecraft and the newer Ocean Color Instrument on the PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) satellite. Researchers note that satellite observation is the only practical way to track a phenomenon operating at this scale across an entire ocean basin, even as its effects are felt very locally along coastlines throughout the Caribbean and Gulf.
This report was published by NASA Earth Observatory on July 29, 2026, drawing on data and analysis from the University of South Florida College of Marine Science.
