Below is a recent photo of Mezcalito's beach. It is on the east side of the island at the intersection of the carretera transversal and the east coast roadway.
Looking on the good side, the Sargassum covers up a lot of the plastic trash that drifts up from South America and the southern Antilles.
There has always been something washing up on Cozumel's coast. In the 1600's, the Quintana Roo Coast (including Cozumel) was known as the "Amber Coast" for the chunks of fossil amber that washed up on its beaches. This amber probably originated in Columbia or Dominican Republic, two countries well known for their amber deposits. Later, intensive mining of these deposits most likely exhausted the sources of the amber that was eroding out or riversides and floating to Cozumel earlier.
In the 1700's and 1800's, shipwrecks were a common event on Cozumel's beaches. Sailing ships were more vulnerable to grounding in storms than today's engine-powered ships, and that period saw a huge increase in trading vessels sailing between the north coast of South America to Cuba and Mexican Gulf Coast ports. Many of these met their end on Cozumel. In my newest book (working on it) I list many of these 18th and 19th century shipwrecks.
In the 1960s and 1970s, petroleum tar was the problem. Tanker ships travelling from the oil producing areas in and near Venezuela were pumping out the oil sludge from their holding tanks and that tar washed up on Cozumel's beaches in an unending stream. If you went to the beach back then, you either carried a bottle of gasoline or thinner with you to clean off the soles of your feet, or ended up with tar smeared all over your floor as you tracked it inside your home or hotel room. Fortunately, laws passed in the 1980's helped stop tankers from pumping out their tanks at sea, and Cozumel's beaches became nearly tar-free soon after.
Next, bales of marijuana and packages of cocaine started washing up on the beach. This led to the Mexican Navy foot and truck patrols. It also led to not a few Cozumel "beachcombers" being arrested for not turning in the packages they found on the beach.
In the past couple of decades, populations exploded along the north coast of South America and the Antilles, resulting in ever-increasing amounts of trash being dumped into the area's rivers and bays. The non-degradable elements of the trash (plastic, etc.) float on the current to land on Cozumel's beaches. No matter how much they pick up these days, more comes to take its place everyday.
Now, it's Sargassum. It's always something. At least it's not tennis shoes with disembodied feet in them, or radioactive debris from Japan!