Record-breaking amounts of sargassum seaweed are inundating the beaches and coastlines of the Caribbean and Gulf of Mexico, causing significant environmental damage and impacting tourism-dependent economies. The thick mats of seaweed are smothering marine life, degrading shorelines, and creating foul odors as they decompose.
Scientists recorded approximately 27 million metric tons of sargassum in the Atlantic, Caribbean, and Gulf of Mexico in July. This year marks the first time large quantities of the algae have been observed growing within these regions, rather than simply being carried in by currents. Brian Barnes, a marine scientist at the University of South Florida, noted that this phenomenon is unusual, stating, "Every year is a little bit of a new story."
The Great Atlantic Sargassum Belt, which has been growing since 2011, has led to increasing amounts of seaweed washing ashore. Experts suggest that factors such as agricultural runoff, warming ocean waters, and changes in wind and current patterns may be contributing to the increased blooms. The current surge follows a record 40 million metric tons reported in the previous year, with the 2025 bloom being so substantial that it initiated a new local reproduction cycle.
In June, sargassum levels in the Caribbean reached historic highs, and the Gulf of Mexico recorded 5 million metric tons, nearly double the previous year's record. Projections indicate that 2026 is expected to see the second-largest amount of sargassum recorded in the Atlantic, Caribbean, and Gulf of Mexico.
Mexico plans to invest $115 million to address the sargassum problem, which threatens both its environment and economy. On the worst days, an estimated 9,000 tons can reach Mexico's Caribbean coast, far exceeding the daily collection capacity of 1,200 tons with current resources.
The economic impact is already being felt in popular tourist destinations like Playa del Carmen. Waiters like Alan Vázquez report closing restaurants early due to a lack of customers, as decomposing sargassum turns the once-clear turquoise waters black. This decline in tourism has led to job losses, with Vázquez's colleagues having been laid off due to a 30% drop in sales in Quintana Roo, a major tourism hub.
Puerto Rico is also experiencing severe sargassum accumulation, particularly in areas like La Parguera. Waldemar Quiles, the U.S. territory's natural resources secretary, expressed concern over the unprecedented concentration of seaweed across multiple locations.
While sargassum in open waters serves as a vital habitat for marine life, its accumulation near shore has detrimental effects. It depletes oxygen, smothers mangrove roots, blocks sunlight essential for coral and seagrass, and can prevent newly hatched sea turtles from reaching the ocean. Efforts to remove the seaweed from beaches can also risk damaging fragile turtle nests.
In the U.S. Virgin Islands, people are having to wade through up to 25 feet of seaweed to reach the water, a situation described by environmental consultant Amy Dempsey as the worst she has seen in five years.
The decomposing seaweed releases toxic gases, including ammonia and hydrogen sulfide, which can cause nausea, headaches, and lung irritation in humans, according to the U.S. Environmental Protection Agency. On the French Caribbean island of Martinique, residents affected by these gases have led to officials opening a temporary shelter.
Researchers from the University of South Florida and the U.S. National Oceanic and Atmospheric Administration have utilized artificial intelligence to analyze macroalgae blooms. Their findings indicate that blooms in the tropical Atlantic and Western Pacific have increased by over 13% annually from 2003 to 2022, covering an area of 16.9 million square miles.