The Outside Story: Otters are some of the river’s strongest swimmers

July 1, 2021  |  By Rey Katz

River otter illustration by Adelaide Murphy Tyrol.

One summer day, I was relaxing on the bank of a secluded pond watching mallard ducks forage when a dark shape broke the stillness of the water. 

It was a North American river otter, swimming with its head and back emerging from the surface, sleek body over 2 feet long, tapered tail trailing behind. 

It dove beneath the surface without a splash. Seconds later, its round head emerged at the edge of the pond. We stared at each other.

Making eye contact with a river otter was a first for me, and likely unusual for the animal as well. River otters (Lontra canadensis) tend to be most active from dusk through dawn. This member of the weasel family will travel large distances through its territory, over land and through water, and can explore up to 20 miles of waterway in search of prey. Otters may hunt and swim together in family groups of a mother and babies or in social groups. They are excellent swimmers, aided by a number of traits that help them maneuver underwater.

“Their bodies are so flexible,” said Margaret Gillespie, a naturalist at Squam Lakes Natural Science Center in New Hampshire. “The way they manipulate themselves is pretty amazing.” 

Otters swim acrobatically, curling and weaving through the water. Using their powerful webbed hind feet and their strong tails, which also help to steer, otters may swim as fast as 8 mph. For comparison, Olympic swimmer Michael Phelps tops out at 5 mph, while a more average human swimmer may reach 2 mph.

River otters have dense fur that provides insulation, and coarse guard hairs that repel water. They are able to close valves in their nose and ears while swimming and diving, and they have a transparent third eyelid, which functions like swimming goggles. At nighttime, in dark or murky water, however, sight becomes less important than touch, and river otters brush their sensitive whiskers through the water and along the bottom of a pond or river feeling for movement – perhaps a crayfish crawling in the mud between rocks. 

Otters mainly hunt fish and shellfish, but they will eat a wide variety of prey including frogs, turtles, birds, and even small mammals. Powerful jaws and sharp teeth crunch through crayfish shells and fish bones. Because catching fish is difficult for river otters in a strong current, they often hunt in still water, including beaver ponds, according to Gillespie. 

In the late 1800s, the beaver population in New Hampshire had been virtually eliminated, in large part due to unregulated harvest during the fur trade and habitat loss. As a result, otter numbers were also dangerously low. As beaver populations recovered in the mid-1900s, and their dams modified the flow of water, the river otter population grew as well. Turtles, amphibians, and muskrats also use beaver ponds – and sometimes become otter prey. 

Otter pups – typically between one and three – are born in late winter, furred, toothless, and with their eyes closed. River otters often raise their young in abandoned beaver lodges. Otter babies can’t swim for the first several weeks of their lives, and reluctant adolescents avoid the water until their mother drags them in when they are about 2 months old. By late spring, however, the pups are foraging with their mother, and by next winter they’ll be on their own.

River otters depend on – and can be indicators of – a healthy and clean ecosystem. Because they are at the top of a long food chain, they may bioaccumulate concentrations of mercury, lead, and PCBs from their prey, which can affect their nervous and endocrine systems, impacting social behavior and pup survival. They may become malnourished if pollution kills their prey. A stable or growing population of river otters is a good indicator that a watershed is thriving: if they are healthy, creatures lower in the food chain are likely doing well.

I felt so lucky to see a river otter that summer day, although the experience was brief. Soon after I spotted it, the otter dove towards the edge of the pond and ran up the bank through thick brush. 

This beautiful animal was a reminder of why we work to conserve wild land and keep waterways clean and free of pollution.

Rey Katz is a writer in Boston. The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of the New Hampshire Charitable Foundation.