I don't know what ship you are sailing, but last year from Cozumel on our Galaxy Panama Canal cruise we took the Catamaran snorkel adventure through the cruiseline. The catamaran took us to a great snorkeling area where I got so caught up in the beautiful sights below that I forgot to pay attention to where I was going and ended 100 yards away from the boat. When I finally came up to see where I was, the crew member was frantically waving and shouting to me. So I swam back to the boat against the waves. Meanwhile, DH stayed on the boat enjoying the free Mexican beer provided. When I got back on the boat, I tried to get the saltwater taste out of my mouth with water, but found that the free margaritas worked better, lol. After snorkeling they took us to their private beach where the beer and margaritas still flowed.
This was a really fun excursion and no one on the cat was feeling any pain afterward. Most people were dancing on deck to the salsa music from the PA system on the way back.
A similar excursion is offered on the Mercury list for our Mexican Riviera cruise coming up in Jan. I am definitely going to sign us up. But this time I will pay closer attention to where I'm going.
I think it's possible to sign up on your own if your cruiseline doesn't offer it. We saw a lot of cats at the beach and I don't think they were all booked through cruises.
1/02 Explorer E.Carib.
1/03 Explorer W. Carib.
8/03 Summit Alaska cruise/tour
2/04 Adventure S. Carib.
2/05 Galaxy Panama Canal
6/06 Jewel Brit. Isles/Nor. Fjords
1/07 Mercury Mexican Riviera
You can also try from Playa Aqua, just a couple of minutes from the turistico and puerta Maya pier or then from the San Francisco Beach club with the glass bottom boat. Check my profile for more information on snorkeling in Cozumel and beaches