Alex Mustard / Blue whale (Balaenoptera musculus) swims beneath the surface of the ocean. Indian Ocean, off Sri Lanka.

Alex Mustard / Blacktip reef shark (Carcharhinus melanopterus) swims through schools of fish. Misool, Raja Ampat, West Papua, Indonesia. Ceram Sea. Tropical West Pacific Ocean.

Alex Mustard / Jellyfish (Catostylus sp.) swims beneath a slick of plastic debris. Indian Ocean off Sri Lanka. Highly commended in the Environmental Report section, Montphoto competition 2019

Alex Mustard / Remoras (Remora sp.) hitchhiking on the tail of a large (13-15m) female whale shark (Rhincodon typus) swims in open water. Wolf Island, Galapagos National Park, Galapagos Islands. East Pacific Ocean.

Alex Mustard / Galapagos green turtle (Chelonia mydas agassizii) swims over a coral reef. Darwin Island, Galapagos National Park, Galapagos Islands. East Pacific Ocean.

Alex Mustard / Striped mackerel (Rastrelliger kanagurta) mouth wide open as it swims through the water, filtering zoopankton with its gill rakers. Marsa Shouna, Port Ghalib, Marsa Alam, Egypt. Red Sea

Sue Daly / Close up of the face of a Brill (Scophthalmus rhombus), swims out of frame, Sark, British Channel Islands, UK, August.

Sue Daly / Close up of a Plaice (Pleuronectes platessa), swims away, Sark, British Channel Islands, UK, June.

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...

Steven Kazlowski / Moose (Alces alces) bull adult swims across a lake in Denali National Park, Interior of Alaska, summer, USA

Nick Upton / Coot (Fulica atra) swims on lake with colourful autumnal tree leaves reflected in the water around its own reflection, Wiltshire, UK, October

Juergen Freund / Snorkeler swims amongst Sergeant major damselfish (Abudefduf vaigiensis) at the house reef of Miniloc Island Resort, El Nido Island, Palawan, Philippines, May 2009. These fish gather in a dense mass w...

Alex Mustard / A Leafy Seadragon (Phycodurus eques) swims over a seagrass bed. Wool Bay Jetty, Edithburgh, Yorke Peninsular, South Australia, November.

Nick Upton / 2020VISION / Northern shoveler drake (Anas clypeata) reflected in calm water as it swims among reeds and rushes in flooded marshland on a sunny winter afternoon. Greylake RSPB reserve, Somerset Levels, UK, January

Alex Mustard / A young California sealion (Zalophus californianus) swims in a shallow pool. Los Isotes, La Paz, Mexico. Sea of Cortez, East Pacific Ocean.

Alex Mustard / Caribbean reef shark (Carcharhinus perezi) swims over a coral reef. Grand Bahama Island, Bahamas. Tropical West Atlantic Ocean.

Alex Mustard / Draughtsboard Shark / Australian Swellshark (Cephaloscyllium laticeps) swims through a giant kelp forest (Macrocystis pyrifera). Like a pufferfish, this species of shark is able to rapidly swell with...

Philip Dalton / Nile Crocodile (Crocodylus niloticus) approaching Common Zebra (Equus burchellii) as it swims across Mara river during migration, Masai Mara GR, Kenya

Philip Dalton / Nile Crocodile (Crocodylus niloticus) grabbing Common Zebra (Equus burchellii) as it swims across Mara river during migration, Masai Mara GR, Kenya

Philip Dalton / Nile Crocodile (Crocodylus niloticus) grabbing Common Zebra (Equus burchellii) as it swims across Mara river during migration, Masai Mara GR, Kenya

Georgette Douwma / Martha Holmes swims with Whale Shark off Hawaii, 1991 on location for BBC NHU television series "Seatrek", Model released

Doug Perrine / Newborn Lemon shark pup swims away from mother {Negaprion brevirostris} Bahamas, Caribbean (Non-ex).

Doug Allan / Weddell seal swims under ice {Leptonychotes weddelli} Antarctica. Weddell seals can dive to a depth of 700m!

Alex Mustard / Hawksbill turtle (Eretmochelys imbricata) male swims infront of a sunburst, near a coral reef. Ras Mohammed National Park, Sinai, Egypt. Red Sea

Alex Mustard / Starck's demoiselle (Chrysiptera starcki) swims above a coral reef. Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Sea.

Tony Wu / Humpback whale calf (Megaptera novaeangliae) male calf peeking out from underneath his pectoral fin as he swims upside-down beneath the ocean surface. His mother was resting about 20 meters below. Vav...

Alex Mustard / Blacktip reef shark (Carcharhinus melanopterus) swims beneath a jetty and schools of silversides (Atherinidae) on a coral reef. Misool, Raja Ampat, West Papua, Indonesia. Ceram Sea. Tropical West Paci...

Alex Mustard / Mimic octopus (Thaumoctopus mimicus) swims over a sandy seabed in a shape considered by some to be a flounder impersonation. Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Sea.

Alex Mustard / Mototi octopus (Amphioctopus mototi) swims across the seabed. Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Sea.

Alex Mustard / Scalloped hammerhead shark (Sphyrna lewini) swims through a school of Pacific creolefish (Paranthias colonus). Wolf Island, Galapagos National Park, Galapagos Islands.. East Pacific Ocean.

Shane Gross / School of Sardines (Clupeidae) swims past a sea fan. Moalboal, Philippines.

Cyril Ruoso / Wels catfish (Silurus glanis) swims away from the riverbank after hunting Feral pigeon (Columba livia) Tarn River, France August

Alex Mustard / A dark coloured Galapagos green turtle (Chelonia mydas agassizii) swims over rocks within a large cave. Punta Vincente Roca, Isabela Island, Galapagos National Park, Galapagos Islands. East Pacific Oc...

Alex Mustard / School of longnose parrortfish (Hipposcarus harid) swims over a coral reef. Ras Mohammed Marine Park, Sinai, Egypt. Red Sea.

Alex Mustard / Hawksbill turtle (Eretmochelys imbricata) swims along a coral reef with pink soft coral (Dendronepthya sp.). Ras Mohammed National Park, Sinai, Egypt. Red Sea.

Alex Mustard / Harlequin hogfish (Bodianus eclancheri) swims on a reef. Punta Vincente Roca, Isabela Island, Galapagos National Park, Galapagos Islands. East Pacific Ocean.

Jen Guyton / Nile crocodile (Crocodylus niloticus) underwater holding a Great white pelican (Pelecanus onocrotalus) prey. after a group of the birds dove into the river to hunt fish. Here, the crocodile slowly sw...

Jen Guyton / Yellow-billed stork (Mycteria ibis) fishing in the Msicadzi River, Gorongosa National Park, Mozambique, while a Nile crocodile (Crocodylus niloticus) swims past. During the dry season many water sour...

Nick Upton / Tufted ducks (Aythya fuligula) and a Coot (Fulica atra) diving to forage in a shallow lake, before a Bewick's swan (Cygnus bewickii) swims in to feed, Gloucestershire, England, UK, December.

Nick Upton / Spiny starfish (Marthasterias glacialis) squeezing into a crevice in a rockpool as a Common prawn (Palaemon serratus) swims past, Cornwall, England, UK, September.

Nick Upton / Mute swan cob (Cygnus olor), preening its wing as it swims, Rutland Water, Rutland, England, UK, November.

Nick Upton / Mallard (Anas platyrhychos) drake drinking as it swims on a lake, Corsham Court, Wiltshire, England, UK, March.

Nick Upton / Great crested grebe (Podiceps cristatus) preening, scratches its head and shakes its feathers as it swims on the surface of a lake, Corsham Court, Wiltshire, England, UK, March.

Nick Upton / Great crested grebe (Podiceps cristatus) preening as it swims on the surface of a lake, leaves frame left, Corsham Court, Wiltshire, England, UK, March.

Sue Daly / Tompot blenny (Parablennius gattorugine), swims out of frame, Sark, British Channel Islands, UK, June.

Sue Daly / Topknot (Zeugopterus punctatus), swims out of the frame, Sark, British Channel Islands, UK, August.

Sue Daly / Bass Dicentrachus labrax, Wide angle, shoal swims by, 2013 , Sark, British Channel Islands, UK,

Nick Upton / Grey seal (Halichoerus grypus) lying on the beach and rolling over in the waves as another seal swims out to sea, Norfolk, England, UK, January.

Nick Upton / Gadwall (Anas strepera) drake calling as it swims on flooded marshland, RSPB Greylake reserve, Somerset Levels, UK, February.

Alex Mustard / Whitetip shark (Carcharhinus longimanus), accompanied by Pilotfish (Naucrates ductor), swims towards the camera as it cruises beneath the surface of the Red Sea, close to Little Brother Island. The Br...

Alex Mustard / Diver swims between impressive speleothem formations, including stalagmites and stalactites, in a freshwater Cenote (or limestone sinkhole). Dream Gate Cenote, Tulum, Quintana Roo, Yucatan, Mexico.

Alex Mustard / Nudibranch (Ceratosoma gracillimum) lays a ribbon of red eggs. while a diver (David Gordon) swims past. Bitung, North Sulawesi, Indonesia. Lembeh Strait, Molucca Sea.

Alex Mustard / Cuckoo wrasse (Labrus mixtus) swims through a kelp forest (Laminaria sp) Porthkerris, Lizard Peninsular, Cornwall, UK August

Alex Mustard / Grey seal (Halichoerus grypus) young male swims over a kelp forest (Laminaria hyperborea) Farne Islands, Northumberland, UK, North Sea, August

Alex Mustard / Grey seal (Haichaoerus grypus) young female swims over granite boulders in the shallows. Lundy Island, Devon, UK. Bristol Channel, August

Alex Mustard / Grey seal (Haichaoerus grypus) silhouetted as it swims at the surface with a sunburst, Lundy Island, Devon, UK, Bristol Channel, August

Alex Mustard / Grey seal (Haichaoerus grypus) large female silhouetted as it swims at the surface with a sunburst, Lundy Island, Devon, UK, Bristol Channel, August

Alex Mustard / Two-spot gobies (Gobiusculus flavescens) school swims over Kelp (Laminaria sp). Porthkerris, Lizard Peninsular, Cornwall, UK, August

Alex Mustard / Majestic / Blue girdled angelfish (Pomacanthus navarchus) swims through hard coral. Kri Island, Raja Ampat, West Papua, Indonesia.

Alex Mustard / Grey seal (Halichoerus grypus) male swims in loops over granite boulders in the shallows. Lundy Island, Devon, UK. Bristol Channel. August

Alex Mustard / John Dory (Zeus faber) swims through a forest of Bootlace weed / Mermaid's hair (Chorda filum) Porthkerris, Lizard Peninsular, Cornwall, UK August

Alex Mustard / Common / harbour seal (Phoca vitulina) swims beneath a kelp forest, Santa Barbara Island, Channel Islands. Los Angeles, California, USA, Pacific Ocean, September

Alex Mustard / Banded / Yellow lipped sea krait (Laticauda colubrina) swims over orange soft coral (Scleronephthya sp) while hunting for prey. Triton Bay, West Papua, Indonesia.

Alex Mustard / Cleaner wrasse (Labroides dimidiatus) swims out from the gill of a Blue spotted pufferfish (Arothron caeruleopunctatus). East of Eden, Similan Islands, Thailand. Andaman Sea, Indian Ocean.

Tony Wu / Humpback whale (Megaptera novaeangliae) calf playing at the surface, while its mother swims beneath, This male has a wound on its abdomen probably caused by a rope or line. Vava'u, Kingdom of Tonga....

Nick Upton / Eurasian beaver (Castor fiber) pair grooming one another at night as one of their kits swims nearby , River Otter, Devon, UK, July. Part of Devon Wildlife Trust's Devon Beaver Trial.

Alex Mustard / School of Crescent-tail bigeyes (Priacanthis hamrur) swims in front of a school of Bigeye jacks (Caranx sexfasciatus). Ulong Island, Rock Islands, Palau, Micronesia. Tropical west Pacific Ocean.

Alex Mustard / Harbor seal (Phoca vitulina) swims through a forest of Giant kelp (Macrocystis pyrifera). Santa Barbara Island, Channel Islands. California, USA. North East Pacific Ocean.

Alex Mustard / Yellow lipped sea snake (Laticauda colubrina) swims on the surface above a shallow coral reef. Yanggefo Island, Gam Island, Raja Ampat, West Papua, Indonesia.

Nick Upton / Seal watching tour boat approaching three adult Grey seals (Halichoerus grypus) resting on offshore rocks at low tide, as another swims nearby, The Carracks, St.Ives, Cornwall, UK, June.

Alex Mustard / Streaming school of Bigeye snappers (Lutjanus lutjanus) swims across a reef filled with fish. Andiamo, Daram Islands, Misool, Raja Ampat, West Papua, Indonesia. Ceram Sea, Pacific Ocean.

Nick Upton / European pochard drake (Aythya ferina) preening as it swims on flooded pastureland, Gloucestershire, UK, January.

Olga Kamenskaya / Diver swims under clear transparent ice (1m thick) with person visible on surface above. Lake Baikal, Russia, March 2012.

Olga Kamenskaya / Diver swims under clear transparent ice (1m thick) with minivan visible above. Lake Baikal, Russia, March 2012.

Olga Kamenskaya / Diver swims under clear transparent ice (1m thick) with minivan and person visible above. Lake Baikal, Russia, March 2012.

Olga Kamenskaya / Diver swims under clear transparent ice (1m thick) with vehicle visible above. Lake Baikal, Russia, March 2012.

Olga Kamenskaya / Diver swims under clear transparent ice (1m thick) with minivan visible above. Lake Baikal, Russia, March 2012.

Brent Stephenson / New Zealand little grebe (Poliocephalus rufopectus) moving across the water as it swims. Waikanae Estuary, Wellington, New Zealand, February. Vulnerable species.

Charlie Summers / Three Tufted Puffin (Fratercula cirrhata) swimming in formation, St. Lazarus National Wildlife Refuge in Sitka Sound, Alaska, August.

Charlie Summers / Brown Bear (Ursus arctos) swimming in the Anan Creek Lagoon of Alaska, July.

Steven Kazlowski / Young polar bear (Ursus maritimus) in slushy icy water, off the 1002 area of the Arctic National Wildlife Refuge, North Slope of the Brooks Range, Beaufort Sea, Alaska, October.

Steven Kazlowski / Young Polar bear (Ursus maritimus) in slushy icy water, off the 1002 area of the Arctic National Wildlife Refuge, North Slope of the Brooks Range, Beaufort Sea, Alaska, October.

Steven Kazlowski / Young polar bear (Ursus maritimus) submerged, swimming in slushy icy water, off the 1002 area of the Arctic National Wildlife Refuge, North Slope of the Brooks Range, Beaufort Sea, Alaska, October.

Steven Kazlowski / Polar bear (Ursus maritimus) subadult submerged in slushy icy water, off Bernard Spit and the 1002 area of the Arctic National Wildlife Refuge, North Slope of the Brooks Range, Beaufort Sea, Alaska, O...

Loic Poidevin / Coypu (Myocastor coypus) swimming, Marais Breton, Brittany / Bretagne, France, April.

Chris & Monique Fallows / Mako Shark (Isurus oxyrinchus), Cape Point, South Africa, April.

Chris & Monique Fallows / Ragged tooth shark (Carcharias taurus), De Hoop, South Africa, January.

Loic Poidevin / Rhinoceros Auklet (Cerorhinca monocerata) adult in water, British Columbia, Canada, June.

Loic Poidevin / Grizzly bear (Ursus arctos horribilis) swimming, Khutzeymateen Grizzly Bear Sanctuary, British Columbia, Canada, June.

Bertie Gregory / Vancouver Island Grey wolf (Canis lupus crassodon) alpha female swimming across estuary, Vancouver Island, British Columbia, Canada, August.

Edwin Giesbers / Oriental small clawed otter (Aonyx cinerea) underwater, captive.

Edwin Giesbers / Oriental small clawed otter (Aonyx cinerea) underwater, captive.

Edwin Giesbers / Oriental small clawed otter (Aonyx cinerea) underwater, captive.