Recently, the Caribbean has been having issues with floating seaweed that covers the beach. The Sargassum Seaweed floats in massive tons and produces a foul smell. Cozumel is a destination that it barely affects.
The Western side of Cozumel is the best area to go. This area is clear and free of Seaweed thanks to channel currents and wind pushing the Sargassum past to Cancun and Playa del Carmen.