Gigantic piles of brown seaweed that reek of rotten eggs are piling up on beaches in the eastern Caribbean, forcing resorts to shut down and keeping swimmers from the ocean. The stinky, bug-infested algae—named Sargassum—has been creeping up shores in Antigua, St. Maarten, and other Caribbean hotspots since June, reports the New York Times. Experts are baffled by the sheer enormity of the seaweed invasion, which has no precedent. The cause remains a mystery, although speculation ranges from natural current shifts to climate change to the Gulf oil spill.
The seaweed does not pose a direct danger to human health, but lifeguards in St. Maarten are still warding off swimmers for fear they could get trapped and drown. The $600-a-night St. James's Club & Villas in Antigua ceased operation for the entire month of September while 10,000 tons of the algae was carted off the beach. The key test comes next year, according to the Times: If the seaweed returns, it could mean that this was no fluke and the sign of a new pattern.