A little more than a 20-minute ride from the cruise ship docked in the port of Cozumel, Mexico, fellow travelers and I stepped from a minivan and practically into the turquoise waters of Dolphin Discovery inChankankanaab National Park.

The Mexican sun baked our backs as we scrambled into snorkels and masks, slipped into new, royal blue life vests, squeezed into fins and trotted from the white-sugar sand to the edge where beach meets water in a well-enclosed lagoon and onto a wooden platform…