Jordi Chias / Woman snorkeller swimming inside lagoon Toau atoll, Tuamotu Archipelago, French Polynesia, Pacific Ocean.

Christophe Courteau / African elephants (Loxodonta africana) swimming across Chobe River, trunks raised above surface for breathing, Chobe National Park, border between Botswana and Namibia.

David Pattyn / Children snorkelling in the sea and swimming with bottlenose dolphins (Tursiops truncatus) with boat approaching. Indian Ocean, Zanzibar, Tanzania, August 2014.

Angelo Gandolfi / Snorkeller with shoal of Piraputanga (Brycon hilarii), Rio Olha d'Agua at Cabeceira do Prata, Bonito, Mato Grosso do Sul, Brazil

Alex Mustard / A fisherman swims down to touch the statue of Christ Of The Abyss (Cristo degli abissi) for good fortune, in the Marine Protected Area of Portofino (Area Marina Protetta, Portofino), Liguria, Italy. M...

Franco Banfi / Two women snorkeling in front of the cave, Raja Ampat, Irian Jaya, West Papua, Indonesia, Pacific Ocean. Model released.

Juergen Freund / Coral reef split level with mangroves with snorkeller, Raja Ampat, West Papua, Indonesia, February 2012 Model released.

Juergen Freund / Woman Snorkler with tropical island in background, split level, Indo-Pacific

Steven David Miller / Snorkler at Blue hole, head spring that feeds Ichetucknee river, Florida, USA, Model released

Juergen Freund / Split level shot of snorkler swimming in clear shallow water over sand, Malaysia.

Gary Bell/ Oceanwide / Snorkler along coast, Christmas Island, Australia

Alex Mustard / Snorkeller looking down on a Blue whale (Balaenoptera musculus) passing beneath. Indian Ocean, off Sri Lanka.

Franco Banfi / Snorkelling the tributary of the Paraguay River, Pantanal, Brazil

Franco Banfi / Photographer Franco Banfi snorkeling in search of fish in the Rio Sucuri, Bonito, Mato Grosso do Sul, Brazil

David Fleetham / Snorkeler diving in shallow water over hard coral reef. Two Tree Island near Kadavu Island, south east Fiji. November 2012. Model released.

Stephane Granzotto / Snorkeller taking pictures of Whale shark (Rhincodon typus) with tracking tag, Tadjourah Gulf, Republic of Djibouti. December, 2017.

Richard Robinson / Snorkeller at North Minerva Reef / Teleki Tokelau a disputed territory in the South Pacific between Tonga and Fiji. January 2015.

Richard Robinson / Snorkeller at North Minerva Reef / Teleki Tokelau a disputed territory in the South Pacific between Tonga and Fiji. January 2015.

Alex Mustard / Young Florida manatee (Trichechus manatus latirostris) plays with a snorkeller. Three Sisters Spring, Crystal River, Florida, USA.

Alex Mustard / Snorkeller rubbing the belly of a baby Florida manatee (Trichechus manatus latirostris). Three Sisters Spring, Crystal River, Florida, USA

Luis Quinta / Snorkeller in Blue shark (Prionace glauca) female off the coast of Portugal. August.

Juergen Freund / Woman swimming with Banded sea kraits (Laticauda colubrina) at low tide, Mali Island, Macuata Province, Fiji, South Pacific

Juergen Freund / Snorkellers swimming around Nudey Beach, Fitzroy Island, Tropical Far North Queensland, Australia. January 2016.

Juergen Freund / Snorkellers swimming around Nudey Beach, Fitzroy Island, Tropical Far North Queensland, Australia. January 2016.

Juergen Freund / Snorkellers swimming the reefs of the Great Barrier Reef, Queensland, Australia October 2016.

Juergen Freund / Snorkellers swimming the reefs of the Great Barrier Reef, Queensland, Australia October 2016.

Juergen Freund / Snorkellers swimming the reefs of the Great Barrier Reef, Queensland, Australia October 2016.

Juergen Freund / Aerial view of snorkellers swimming the reefs of the Great Barrier Reef, Queensland, Australia October 2016.

Juergen Freund / Aerial view of the reefs of the Great Barrier Reef showing the tourist dayboats, Great Barrier Reef, Queensland, Australia October 2016.

Juergen Freund / Aerial view of snorkellers swimming the reefs of the Great Barrier Reef, Queensland, Australia October 2016.

Juergen Freund / Split level of snorkellers swimming the reefs of the Great Barrier Reef underwater, Great Barrier Reef, Queensland, Australia October 2016.

Juergen Freund / Snorkellers swimming the reefs of the Great Barrier Reef with a semi-submesible carrying tourists to see the reef from underwater, Great Barrier Reef, Queensland, Australia October 2016.

Juergen Freund / Snorkellers swimming the reefs of the Great Barrier Reef with a semi-submesible carrying tourists to see the reef from underwater, Great Barrier Reef, Queensland, Australia October 2016.

Juergen Freund / Snorkellers swimming the reefs of the Great Barrier Reef with a semi-submesible carrying tourists to see the reef from underwater, Great Barrier Reef, Queensland, Australia October 2016.

Juergen Freund / Snorkeler videos the coral bleaching in the northern Great Barrier Reef. On 10 March 2017 the Great Barrier Reef Marine Park Authority confirmed mass coral bleaching is occurring on the Great Barrier...

Juergen Freund / Snorkeler videos the coral bleaching in the northern Great Barrier Reef. On 10 March 2017 the Great Barrier Reef Marine Park Authority confirmed mass coral bleaching is occurring on the Great Barrier...

Alex Mustard / Snorkeller swimming through Golden jellyfish (Mastigias sp.) in a marine lake, Jellyfish Lake, Eil Malk island, Rock Islands, Palau. Tropical north Pacific Ocean.

Alex Mustard / Woman snorkeling over a coral reef that is reflected on the surface. Sha'ab El Erg, Hurghada, Egypt. Red Sea. Model released.

Michel Roggo / Underwater view pf photographer Michel Roggo snorkelling in Anhumas Abyss Bonito area, Serra da Bodoquena (Bodoquena Mountain Range), Mato Grosso del Sul, Brazil. November 2012 . Photographed for The...

Michel Roggo / Photographer Michel Roggo snorkelling in the Sense river, Cantons of Fribourg and Bern, Switzerland. July. Photographed for The Freshwater Project.

Franco Banfi / Woman snorkeling near beach, Seychelles, Indian Ocean.

Franco Banfi / Woman snorkeling near a beach, Seychelles, Indian Ocean.

Inaki Relanzon / Green turtle (Chelonia mydas) swimming with snorkelers in the background, Canary Islands, Spain, July.

Alex Mustard / Two snorkellers swim in the water of a Cenote (a freshwater sink hole), while sun light filters down through the leaves of a red mangrove tree (Rhizophora mangle). Casa Cenote, Tulum, Quintana Roo Yuc...

Doug Perrine / Woman swimming with Hawaiian / Gray's Spinner Dolphins (Stenella longirostris longirostris), off Ho'okena Beach, South Kona, Hawaii, USA, Central Pacific Ocean. Model released

Pascal Kobeh / Snorkeler in front of the Arch among the rocky islands, Koror, Palau, Philippine Sea

Pascal Kobeh / Whale shark (Rhincodon typus) mouth wide open, feeding on plankton close to the surface with snorkelers nearby, Yucatan Peninsula, Mexico

Franco Banfi / Free diver swimming over a field of green algae moving in the current of Litlaa 'Little River', northern Iceland

Franco Banfi / Snorkeling over multicoloured sediments leaping from the bottom at Litlaaa 'Little River', northern Iceland

Tony Wu / Man holding up fresh Pygmy blue whale (Balaenoptera musculus brevicauda) faeces. The brilliant orange-red color derives from krill diet of the cetacean. Sri Lanka, Indian Ocean.

Alex Mustard / Snorkeller swimming over a shallow coral reef with a large stand of Staghorn coral (Acropora cervicornis). North Wall, Grand Cayman, Cayman Islands, British West Indies. Caribbean Sea. Critically enda...

Pete Oxford / Snorkeller collecting edible algae (Eucheuma sp.) Lighthouse Reef Atoll. Belize. May 2015.

Solvin Zankl / Algae scientist studying invasive Japanese wireweed (Sargassum muticum) Norway, May 2015.

Claudio Contreras / Freediver in sinkhole, Cenote Siete Bocas, near Puerto Morelos, Riviera Maya, Yucatan Peninsula, Mexico. April

Constantinos Petrinos / Young boy snorkelling over hard corals (reef-building corals) Sharm el Sheikh, Red Sea, Egypt, October 2010. Model released

Pascal Kobeh / Split level view of 'Barnacle' artificial reef with scuba diver. Built in 1997 with a steel frame using mild electric currents to encourage coral growth. Ihuru Island in North Male Atoll, Maldives,...

Pete Oxford / Cape gannet (Morus capensis) diving underwater with snorkelers behind,Eastern Cape, South Africa. Vulnerable. Endemic to Southern Africa

Pascal Kobeh / Bottlenose dolphins (Tursiops truncatus) swimming in open water with two snorkellers around them, Reunion Island. Indian Ocean. October 2009.

Pascal Kobeh / Young boy and an adult snorkeling at the surface above a group of spinner dolphins (Stenella longirostris) Egypt. Red Sea. June 2010.

Pascal Kobeh / Snorkler with a male green turtle (Chelonia mydas) Mayotte. Indian Ocean.

Michael Pitts / Tracking shot over bleached Table coral (Acropora) towards a man snorkelling, Maldives, Indian Ocean.

Franco Banfi / Photographer Franco Banfi snorkelling in search of fish in the Rio Sucuri, Bonito, Mato Grosso do Sul, Brazil

Franco Banfi / Woman snorkeling at Rukavac beach, Vis Island, Croatia, Adriatic Sea, Mediterranean

Franco Banfi / Woman snorkeling in front of the beach of Komiza, Vis Island, Croatia, Adriatic Sea, Mediterranean

Franco Banfi / Woman snorkeling in front of the beach of Komiza, Vis Island, Croatia, Adriatic Sea, Mediterranean

Franco Banfi / Two women snorkeling in front of the cave, Raja Ampat, Irian Jaya, West Papua, Indonesia, Pacific Ocean

Juergen Freund / Woman Snorkler swimming over coral reef, Underwater Indo-Pacific

Juergen Freund / Snorkler diving down to view coral reef, Great Barrier Reef, Queensland, Australia

Juergen Freund / Snorkler collecting Crown of thorns starfish {Acathaster planci} Underwater Indo-Pacific

Juergen Freund / Split level of snorkler diving over coral reef near island, Palawan, Phillippines

Jeff Rotman / Snorkler swims beside wild Bottlenose dolphin (Tursiops truncatus) at night, Red Sea, Egypt Model released.

Jeff Rotman / Snorkler interacts with Bottlenose dolphin {Tursiops truncatus} Nuweiba, Red Sea, Egypt. Model released.

Juergen Freund / Australian sea lion {Neophoca cinerea} underwater with snorkler, Fisherman's Island, Batavia Coast, Western Australia

Juergen Freund / Australian sea lions {Neophoca cinerea} underwater with snorkler, Fisherman's Island, Batavia Coast, Western Australia

Juergen Freund / Snorkler watching Box jellyfish {Chiropsalmus sp.} Queensland, Australia 2006

Juergen Freund / Snorkler looking at Box jellyfish {Chiropsalmus sp.} Queensland, Australia 2006

Juergen Freund / Snorkler looking at Box jellyfish {Chiropsalmus sp.} Queensland, Australia 2006

Juergen Freund / Snorkler on tow line, behind 'Undersea Explorer' boat, watching Dwarf minke whale {Balaenoptera acutorostrata} Queensland, Australia

Juergen Freund / Snorkler on tow rope watching Dwarf minke whale {Balaenoptera acutorostrata} Queensland, Australia

Juergen Freund / Dwarf minke whale {Balaenoptera acutorostrata} investigating snorkler on tow line, Queensland, Australia

Juergen Freund / Australian sea lion {Neophoca cinerea} underwater with snorkler watching, Fisherman's Island, Batavia Coast, Western Australia

Juergen Freund / Dwarf minke whale {Balaenoptera acutorostrata} investigating snorkler, Queensland, Australia

Juergen Freund / Dwarf minke whale {Balaenoptera acutorostrata} surfacing next to snorkler, Queensland, Australia

Juergen Freund / Dwarf minke whale {Balaenoptera acutorostrata} head rising beside snorkler being towed by rope, Queensland, Australia

Doug Perrine / Whale shark {Rhincodon typus} and snorkler, Kona Coast, Hawaii

Doug Perrine / Whale shark {Rhincodon typus} with snorkler, Kona Coast, Hawaii

Steven David Miller / Snorkler at entrance to Devil Cave system, head of Ginnie springs, Florida, USA

Steven David Miller / Snorkler at entrance to Devil's Ear spring, Florida, USA

Doug Perrine / Snorkler swimming over Bimini Road, Bahamas - blocks of natural beach rock or a lost city?

Juergen Freund / Snorkler and cottages of El Nido resort, Philippines

Jeff Rotman / Diver swimming with Manta ray {Manta birostris} Pacific, Mexico

Juergen Freund / Snorklers swim with Whale shark {Rhincodon typus} Donsol, Philippines 2002

Juergen Freund / Woman snorkeling in front of tropical island, Australia. Cocos Keeling Is.

Jeff Rotman / Manta ray with diver {Manta birostris} Soccora Is, Mexico, Pacific

Jeff Rotman / Manta ray with diver {Manta birostris} Soccora Is, Mexico, Pacific

Gary Bell/ Oceanwide / Snorkler along coast, Christmas Island, Australia