Sargassum is a floating seaweed native to the Atlantic, first documented in the 15th century when Christopher Columbus spotted patches of it in the Sargasso Sea. It traditionally stayed offshore, providing a floating habitat for marine life. In 2011 satellites spotted a vast belt stretching from the Caribbean to West Africa. The blooms have grown bigger every summer since. Scientists suspect a warming climate and increased agricultural runoff are driving the surge.
In May 2025 an estimated 38m tonnes of sargassum lurked in the Caribbean and neighbouring parts of the Atlantic. When it washes ashore it turns beaches brown and, as it decays, releases hydrogen sulphide and ammonia—gases toxic enough to force schools in Martinique to close. The tough, spiny fronds damage fishing gear and reduce catches. Piles of weed block turtles from reaching nesting sites and ensnare hatchlings. In Mexico, removing sargassum costs between $300,000 and $1.5m per kilometre of beach.
Some companies are trying to turn the problem into a resource. Seafields, a company using satellite images and drones, corrals floating sargassum into flexible open-water "paddocks" before it reaches shore, keeping it alive and odour-free until it can be harvested. BioPlaster, a Mexican materials company, has developed a sargassum-based alternative to cling film and plastic bags. Farmed seaweeds like kelp are already used in bioplastics, biofuels and livestock feed, but sargassum supply remains too unpredictable to serve as a viable feedstock.
I am an optimist. It does not seem too much use being anything else.