This thread is about diving and snorkeling.

Believe whom you wish, verify with personal experience. As a master diver with sixty years of scuba diving and longer than that snorkeling, in well over three dozen countries, I can tell you snorkeling and sand beaches generally don't go well together.

There is good snorkeling on Cozumel, just not off beaches unless the wind and sea conditions are favorable. But the sand beach / pretty unsettled outside of the island isn’t settled and dived regularly because that’s the side that is the windward side, open to the Caribbean Sea and waves. The settled leeward side is sheltered and on the channel facing the mainland.

There is a very long beautiful wind swept beach on the ocean side of Cozumel that is often affected by currents and waves - sufficiently so dive boats generally don't go there because of the difficult conditions. Snorkeling wouldn't be much good there except under favorable conditions. Hanging out on the beach would be.

There are a few other beaches on the Yucatán Channel side, but you'll mostly find them to be extremely crowded - some have dining and recreation facilities and have bus loads of cruise ship passengers brought to them on shored trips.