George Sanker / North American river otter (Lontra canadensis) swimming with head above water. Acadia National Park, Maine, USA. November.

George Sanker / North American river otter (Lontra canadensis) two in water with autumnal trees reflected in the water, Acadia National Park, Maine, USA, October.

George Sanker / North American River Otter (Lontra canadensis) two swimming near the surface with autumn leaves reflected in water, Acadia National Park, Maine, USA, October.

Mark Carwardine / Northern / North American river otter (Lontra canadensis) swimming, Captive, Slimbridge, Gloucestershire, UK, July

Michael Quinton / North American River Otter (Lontra canadensis) on iced over river, Yellowstone National Park, Wyoming

Nick Garbutt / North American river otter (Lutra canadiensis), two standing at edge of frozen Upper Yellowstone River, Hayden Valley, Yellowstone, USA. February.

Danny Green / North American otter (Lontra canadensis) eating a fish, Yellowstone National Park, USA, February

John Cancalosi / Three River otters (Lutra canadensis) rolling, scratching and grooming itself on a log, Wyoming, USA, July.

John Cancalosi / River otter (Lutra canadensis) rolling, scratching and grooming itself on a log, Wyoming, USA, July.

John Cancalosi / River otter (Lutra canadensis) feeding on a Cutthroat trout (Oncorhynchus clarkii), Wyoming, USA, July.

John Cancalosi / River otter (Lutra canadensis) feeding on a Cutthroat trout (Oncorhynchus clarkii), Wyoming, USA, July.

John Cancalosi / River otter (Lutra canadensis) feeding on Cutthroat trout (Oncorhynchus clarkii), Wyoming, USA, July.

John Cancalosi / Two River otters (Lutra canadensis) resting on a log, one grooming and scratching itself, Wyoming, USA, July.

John Cancalosi / River otter (Lutra canadensis) feeding on Cutthroat trout (Oncorhynchus clarkii), Wyoming, USA, July.

John Cancalosi / River otter (Lutra canadensis) grooming and settling to rest, Wyoming, USA, July.

John Cancalosi / River otter (Lutra canadensis) feeding on Cutthroat trout (Oncorhynchus clarkii), Wyoming, USA, July.

John Cancalosi / River otter (Lutra canadensis) feeding on Cutthroat trout (Oncorhynchus clarkii), Wyoming, USA, July.

George Sanker / North American river otter (Lontra canadensis) emerging from water, Acadia National Park, Maine, USA, October.

Roger Powell / North American river otters (Lontra canadensis) family group with one of which has just caught a crab, Lower Suwannee River, Levy County, Florida, USA April

Will Burrard-Lucas / North American river otter (Lontra canadensis), group exploring the banks of river. Grand Teton National Park, USA. May

Edwin Giesbers / North American river otter (Lutra canadensis) captive, occurs in North America.

Paul Hobson / North American river otter (Lontra canadensis) playing in snow, Yellowstone National Park, Wyoming, USA, February.

Paul Hobson / North American river otter (Lontra canadensis) playing in snow, Yellowstone National Park, Wyoming, USA, February.

Paul Hobson / North American river otter (Lontra canadensis) playing in snow, Yellowstone National Park, Wyoming, USA, February.

Paul Hobson / North American river otter (Lontra canadensis) playing in snow, Yellowstone National Park, Wyoming, USA, February.

Sean Crane / North American River Otter (Lontra canadensis) trio on ice, Muscatatuck National Wildlife Refuge, Indiana

George Sanker / North American River Otter (Lontra canadensis) on ice in a beaver pond. Acadia National Park, Maine, USA, November

George Sanker / North American River Otters (Lontra canadensis) on ice in a beaver pond. Acadia National Park, Maine, USA, November

George Sanker / North American River Otter (Lontra canadensis) looking up curiously in a beaver pond. Acadia National Park, Maine, USA, November

Charlie Summers / Northern River Otter (Lontra canadensis) resting on the banks of Gibbon River, Yellowstone National Park, Wyoming.

Sumio Harada / North American River Otter (Lontra canadensis) pair on frozen river, Yellowstone National Park, Wyoming

Sumio Harada / North American River Otter (Lontra canadensis) family on frozen river, Yellowstone National Park, Wyoming

David Kjaer / Three North American / Canadian Otters (Lutra canadensis) lying on each other by water. Captive, UK.

Diane McAllister / Canadian river otter (Lutra canadensis) on a log enjoying its evening meal of a Cutthroat trout, starting at the tail. Trout Lake, Yellowstone National Park, Wyoming, USA, June

Diane McAllister / Canadian river otter (Lutra canadensis) on a log enjoying its evening meal of a Cutthroat trout, starting at the tail. Trout Lake, Yellowstone National Park, Wyoming, USA, June. Winner of the Amateur...

Brent Stephenson / Fully grown Northern River Otter (Lutra canadensis) pup swimming along the shoreline. Walker Cove, Alaska, United States, July.

Mark Carwardine / Two Northern / North American river otters (Lontra canadensis) swimming, Captive, Slimbridge, Gloucestershire, UK, July

Mark Carwardine / Northern / North American river otter (Lontra canadensis) on tree trunk at edge of pool of water, Captive, Slimbridge, Gloucestershire, UK, July

John Cancalosi / Canadian otter / North American river otter (Lontra / Lutra canadensis) feeding on a crayfish. Wyoming, USA, July 2010

Matthias Breiter / North American River Otter (Lontra canadensis) family, Sitka, Alaska

Matthias Breiter / North American River Otter (Lontra canadensis) with crab prey, San Juan Island, Washington

Michael Quinton / North American River Otter (Lontra canadensis) pair swimming, Prince William Sound, Alaska

Michael Quinton / North American River Otter (Lontra canadensis) swimming, Alaska

John Cancalosi / Canadian Otter (Lutra canadensis) in shallow river, hunting for fish, Wyoming, USA

John Cancalosi / Canadian Otter (Lutra canadensis) licking a Lichen covered log over a river, Wyoming, USA

John Cancalosi / Canadian Otter (Lutra canadensis) feeding on fish in river, Wyoming, USA

John Cancalosi / Canadian Otter (Lutra canadensis) eating fish, Wyoming, USA

John Cancalosi / Canadian Otter (Lutra canadensis) swimming in shallow river, hunting for fish, Wyoming, USA

John Cancalosi / Canadian Otter (Lutra canadensis) portrait on river bank, Wyoming, USA

John Cancalosi / Canadian Otter (Lutra canadensis) portrait standing in shallow river, Wyoming, USA

John Cancalosi / Canadian Otter (Lutra canadensis) feeding on fish, on river bank, Wyoming, USA, July

John Cancalosi / Canadian Otter (Lutra canadensis) swimming in shallow river, hunting for fish, Wyoming, USA

John Cancalosi / Canadian Otter (Lutra canadensis) swimming in river, Wyoming, USA

Hiroya Minakuchi / North American River Otter (Lontra canadensis) family, Prince William Sound, Alaska

ZSSD / North American River Otter (Lontra canadensis) on the lookout, native to North America

Patricio Robles Gil / North American river otter (Lutra canadensis) on frozen river near a waterfall, Yellowstone National Park, Wyoming, USA, February 2006

Matthew Maran / Canadian River Otter {Lutra canadensis} climbing through a hole to look for fish scraps on a moored fishing boat, Barkley Sound, Vancouver Island, BC, Canada

Jeff Vanuga / Canadian / Northern River Otter (Lutra canadensis) on ice shelf in the Snake River, Wyoming, USA

Eric Baccega / Canadian otter (Lutra canadensis) diving, British Columbia, Canada

Eric Baccega / Canadian otter (Lutra canadensis) diving, British Columbia, Canada

Eric Baccega / Canadian otter (Lutra canadensis) diving, British Columbia, Canada

Colin Seddon / North American / Canadian otter {Lutra canadensis} swimming, UK captive

Colin Seddon / North American / Canadian otter {Lutra canadensis} swimming, UK captive

Colin Seddon / North American / Canadian otter {Lutra canadensis} 12-week cub and bitch, captive, UK

Tim Fitzharris / North American River Otter (Lontra canadensis) eating a fish, North America

John Cancalosi / Canadian River Otter (Lutra canadensis) feeding on Cutthroat Trout (Oncorhynchus clarkii) Montana, USA

John Cancalosi / Canadian River Otter (Lutra canadensis) feeding on Cutthroat Trout (Oncorhynchus clarkii) Montana, USA

Mary McDonald / Canadian otter feeding on fish (Lutra canadensis) captive

George McCarthy / Northern River Otter (Lutra canadensis) Yellowstone NP, Montana, USA

George McCarthy / Northern river otters {Lutra canadensis} swimming in Snake River, Grand Teton NP, Wyoming, USA

George McCarthy / Northern River Otter (Lutra canadensis) on the bank of the Madison River in Yellowstone NP, Montana, USA

George McCarthy / Family group of Northern River Otters (Lutra canadensis) on the bank of the Madison River in Yellowstone NP, Montana, USA

George McCarthy / Northern River Otter (Lutra canadensis) on the bank of the Madison River in Yellowstone NP, Montana, USA

George McCarthy / Northern River Otter (Lutra canadensis) on the bank of the Madison River in Yellowstone NP. Montana, USA

ZSSD / North American River Otter (Lontra canadensis) pair, North America

LYNN M. STONE / Canadian river otter {Lutra canadensis} USA

Mary McDonald / Canadian river otter {Lutra canadensis} feeding on fish, Canada captive

LYNN M. STONE / Canadian otter {Lutra canadensis} feeding on fish, USA

LYNN M. STONE / Canadian otter (Lutra canadensis) beside river, Montana, USA

TOM MANGELSEN / Canadian otters grooming on log (Lutra canadensis) Montana, USA.

TOM MANGELSEN / Canadian otter standing on ice (Lutra canadensis) Montana, USA.

Jeff Vanuga / River otter {Lutra canadensis} emerging from thermal hole in Yellowstone NP, USA.

Gerry Ellis / North American River Otter (Lontra canadensis) portrait with head out of water, Sub-arctic Aquatic, North America

Gerry Ellis / North American River Otter (Lontra canadensis) pair, North America

Konrad Wothe / North American River Otter (Lontra canadensis) swimming underwater, North America

Gerry Ellis / North American River Otter (Lontra canadensis) mother and baby, North America

Sumio Harada / North American River Otter (Lontra canadensis) on ice at water's edge, Yellowstone National Park, Wyoming

Sumio Harada / North American River Otter (Lontra canadensis) on ice at water's edge with fish in paws, Yellowstone National Park, Wyoming

Michael Quinton / North American River Otter (Lontra canadensis) three in snow, western Montana

Michael Quinton / North American River Otter (Lontra canadensis) family resting on submerged log in the spring, Montana

Michael Quinton / North American River Otter (Lontra canadensis) pair along river bank in the fall, Yellowstone National Park, Wyoming

Michael Quinton / North American River Otter (Lontra canadensis) breaking through river ice while fishing in the spring, Yellowstone National Park, Wyoming

Michael Quinton / North American River Otter (Lontra canadensis) pair along river bank in snow, Yellowstone National Park, Wyoming

Michael Quinton / North American River Otter (Lontra canadensis) group along snow-covered river bank, Salmon River, Wyoming

Michael Quinton / North American River Otter (Lontra canadensis) trio running along river bank in winter, Salmon River, Idaho