The island of Barbados declared a national emergency in August because of the seaweed invasion.
The seaweed can pile up to 7 meters thick (over 22 feet) on coastlines.
"We've had mass mortality of sea turtles that have gotten trapped under ever-thickening piles," Hazel Oxenford, a Barbados-based fisheries biologist at the University of the West Indies, told The New Republic. "When the turtles try to come up for air, they drown."
In its natural habitat in the Sargasso Sea, the floating algae provides a habitat for fish and crustaceans, which seabirds and sharks then feed on.
Researchers struggling to understand these Sargassum blooms have said more research is needed, especially into the role of nitrogen pollution and ocean acidification.
"The issue is that we never know what it's going to be like — we can have a week or two weeks where it's very clear and then all of a sudden overnight it washes in," Larry Basham, chief operating officer of Elite Island Resorts, told the BBC.