The mention of Caribbean beaches conjures up images of pristine stretches of white sand and crystal-clear turquoise waters, but an infestation of algae along Mexico’s Caribbean coastline is threatening that reputation. Sargassum, a type of brown algae, is covering the beaches, turning the water brown, and emitting a strong and unpleasant smell resembling rotten eggs as it decomposes. According to the BBC, around 621 miles of Mexican beaches have been heavily impacted by sargassum this year, including popular destinations like Cancun, Playa del Carmen, and Tulum.

The Associated Press reported that sargassum might do more than just ruin tourists’ vacations on which the local economy relies. As the algae decomposes, it falls to the bottom of the sea and smothers the coral. The large amount of algae on beaches, despite locals trying to shovel it away regularly (in vain), also prevents turtles from nesting.

Caribbean beaches affected by sargassum. Photo: Sargassum Monitoring

Mexico is not the only spot that has to deal with the devastating algae; AP explained that all the islands and mainland beaches in the Caribbean are touched by the infestation. Check out Sargassum Monitoring‘s maps of the beaches affected before booking your vacations.