These Mayan guys will take you out to the coral reef (which is fantastic btw) about 1 km out from the beach. They provide you with snorkel masks and flippers and keep an eye on you while you jump in and check out the amazing corals and other sea life. I had planned myself to go out on one of these boats at some point. But as it happened I got in with a young Mexican guide who for a fair bit less than these boatmen charge drove me up the coast a few miles where the reef comes into a mere 100 yards away from the beach. So the two of us plus an American couple simply swam out to the reef under our own steam. What I saw there was truly amazing. Fiirst time proper snorkling for me. It's like a fantasy world down there only its real. If you've never snorkeled on a reef before give yourself a treat sometime if you get the opportunity. It's magic!