Sargassum, a type of brown floating algae, has shifted its range in recent decades, thinning out in the North Atlantic’s Sargasso Sea while proliferating in the tropical Atlantic. That trend, underway since 2011, continued in 2026 as the algae, commonly known as a type of seaweed, reached its annual peak in June across a stretch of ocean known as the Great Atlantic Sargassum Belt.
The belt’s Sargassum abundance in June 2026 made it the second-highest Sargassum year in the satellite record, slightly behind 2025, according to scientists at the University of South Florida (USF) College of Marine Science. Regionally, the Caribbean Sea and the Gulf of America (Gulf of Mexico) both hit record highs, according to USF’s June 2026 Sargassum outlook. The western and eastern Caribbean saw 3.6 and 9 million metric tons, respectively, while the Gulf saw 5 million metric tons—nearly double its previous record, also set in 2025.
“The belt is a basin-scale phenomenon that can have devastating local-scale impacts throughout the Caribbean and Gulf, and satellite observations are the only method that captures both scales on a daily basis,” said Brian Barnes, a marine scientist at the Optical Oceanography Laboratory at USF. “The tracking done by our lab helps communities know the current extent of Sargassum and prepare for what's to come.”
