Dan Burton / Snorkeler over coral reef Sharm el Sheik Red Sea Egypt

Jeff Rotman / Snorkelers at coral reef Red Sea Model released.

Juergen Freund / Snorkeler collecting Crown of thorns starfish {Acanthaster planci} Indo-pacific

Franco Banfi / Snorkeler swimming over coral reef with shoal of Chromis (Chromis sp.), Pescador Island, Moalboal, Cebu Island, Central Visayas, Philippines, Pacific Ocean.

Shane Gross / Whale shark (Rhincodon typus) swimming close to surface accompanied by three Pilot fish (Naucrates ductor) with snorkeler swimming above, La Ventana, Baja California, Sea of Cortez, Mexico. Endangered...

D. Parer & E. Parer-Cook / Humpback Whale (Megaptera novaeangliae) males chasing female during heat run near snorkeler, Tonga

Shane Gross / Humpback whale (Megaptera novaeangliae) surfacing next to snorkeler, Tubuai, French Polynesia, Pacific Ocean.

Shane Gross / Humpback whale (Megaptera novaeangliae) swimming next to snorkeler, Tubuai, French Polynesia, Pacific Ocean.

Shane Gross / Humpback whale (Megaptera novaeangliae) swimming below water surface with snorkeler in the background, Tubuai, French Polynesia, Pacific Ocean.

Roland Seitre / Hawaiian Monk Seal (Monachus schauinslandi) and snorkeler, Hanauma Bay, Oahu, Hawaii

David Fleetham / Snorkeler swimming over coral heads close to the shore off Kandavu Island, Fiji, Pacific Ocean. Model released.

Luciano Candisani / Haenyeo, a traditional fishing diver, diving, Jeju Island, South Korea

Luciano Candisani / Octopus collected by Haenyeo, a traditional fishing diver, Jeju island, South Korea

Luciano Candisani / Haenyeo, a traditional fishing diver, Jeju Island, South Korea

Luciano Candisani / Haenyeo, a traditional fishing diver, with catch, Jeju Island, South Korea

Luciano Candisani / Haenyeo, a traditional fishing diver, with catch, Jeju Island, South Korea

Luciano Candisani / Haenyeo, a traditional fishing diver, diving, Jeju Island, South Korea

Luciano Candisani / Haenyeo, a traditional fishing diver, with catch, Jeju Island, South Korea

Luciano Candisani / Haenyeo, a traditional fishing diver, with catch, Jeju Island, South Korea

Luciano Candisani / Haenyeo, a traditional fishing diver, with catch, Jeju Island, South Korea

Luciano Candisani / Haenyeo, a traditional fishing diver, diving, Jeju Island, South Korea

Luciano Candisani / Haenyeo, a traditional fishing diver, diving, Jeju Island, South Korea

Luciano Candisani / Haenyeo, a traditional fishing diver, Jeju Island, South Korea

Luciano Candisani / Haenyeo, a traditional fishing diver, with catch, Jeju Island, South Korea

Tui De Roy / Galapagos Sea Lion (Zalophus wollebaeki) and Green Sea Turtles (Chelonia mydas) with tourists, Punta Espinosa, Fernandina Island, Galapagos Islands, Ecuador

Tui De Roy / Marine Iguana (Amblyrhynchus cristatus) and tourist, Punta Espinosa, Fernandina Island, Galapagos Islands, Ecuador

Franco Banfi / Snorkeler and fin whale (Balaenoptera physalus) Pelagos Sanctuary for Mediterranean Marine Mammals, Mediterranean Sea. September

Franco Banfi / Snorkeler swimming with Loggerhead turtle (Caretta caretta) accompanied by pilotfish (Naucrates ductor) swimming near the surface. Santa Maria Island, Azores, Portugal, Atlantic Ocean. Vulnerable.

Juergen Freund / Snorkeler amongst Golden jellyfish (Mastigias papua etpisoni) in marine lake, split level image with mangrove forest on shore. Millions of the jellyfish migrate horizontally across the lake daily. Sub...

Juergen Freund / Snorkeler exploring reef, aerial view. Raja Ampat Islands, West Papua, Indonesia. 2018.

Juergen Freund / Snorkeler exploring coastal reef, aerial view. Raja Ampat Islands, West Papua, Indonesia. 2018.

Shane Gross / Snorkeler inspects a large patch of dead Elkhorn coral (Acropora palmata) in The Bahamas. Climate change and pollution have lead to coral reefs dying unprecedented rates.

Shane Gross / Oceanic whitetip shark (Carcharhinus longimanus) and snorkeler with camera off Cat Island, Bahamas. Non-ex