Palancar Gardens, El Cielito and Colombia Deep Reef Snorkelling Tour, Cozumel Island, Quintana Roo State, Mexico

Underwater photo taken during the Palancar Gardens, El Cielito and Colombia Deep Reef Snorkelling Tour, Cozumel Island, Quintana Roo State, Mexico

A myriad of hard and soft corals compete for space on the substrate of the snorkel site known as the Milky Way, Palau, Micronesia, Pacific

Snorkeling woman holding starfish underwater, The Maldives, Indian Ocean

Horse-eye jacks (Caranx latus), schooling in Hol Chan Marine Preserve, inside the Mesoamerican Barrier Reef, Belize

Southern stingray (Hypanus americanus), with snorkeler in shark and ray alley, Caye Caulker, Mesoamerican Barrier Reef, Belize

Southern stingray (Hypanus americanus) being fed in shark and ray alley, Caye Caulker, Mesoamerican Barrier Reef, Belize

Green sea turtle (Chelonia mydas), with snorkeler near Caye Caulker, inside the Mesoamerican Barrier Reef, Belize

Sign warning against feeding sharks, Half Moon Caye, Mesoamerican Barrier Reef, Belize

Underwater view of the reef along the circumference of the Great Blue Hole on Lighthouse Reef, UNESCO, Belize

Hector's dolphins (Cephalorhynchus hectori) by swimmer. Akaroa, New Zealand.

Thrill seekers experience cage diving with Galapagos sharks, Carcharhinus galapagensis, North shore, Oahu, Hawaii, USA

Young woman snorkeling with a school of fish, Water Cay, Utila, Honduras

Snorkeling in Shark Alley and Hol Chan Marine Reserve, Ambergris Cay, Belize