University of Illinois Extension

Wildlife Directory

River Otter ( Lontra canadensis )

Mustelidae
River otters (Lontra canadensis) can be distinguished from beaver and muskrats by their stout, furred tail. Photo courtesy of Tim Daniel, Ohio Department of Natural Resources (IDNR image library)

Did You Know?

  • River otters are the largest member of the weasel family in Illinois.
  • In the late 1980s, there may have been as few as 100 river otters left in Illinois, but today, river otters can be found in every county.

Description and Identification

River otters are long, streamlined mammals. They can be distinguished from muskrat and beaver by the stout, tapered, furred tail. A broad, flattened head, prominent nose, long, bristly whiskers, small rounded ears, small eyes, and thick neck are other characteristics used to identify river otters. The legs of a river otter are short with five webbed toes on each foot. River otters are dark brown to nearly black with pale brown or gray undersides. They weigh 10 to 30 pounds and are 34 to 53 inches long from nose to tip of tail.

Tracks

River otter have a loping gait when on land. Their tracks are approximately 2½ to 3½ inches wide, and the webbing and claw marks are often visible. On snow or ice, otters use a bound-slide form of locomotion. In snow, their tracks are interspersed with 10- to 20-foot slide marks.

Droppings

River otters deposit their droppings (scat) in prominent locations near water, such as on a log or rock. One to many otters will use the same latrine area (known as spraints) many times. Fresh otter scat is dark and contains fish scales and bones or the remains of other food items.

Habitat

River otters can be found in rivers, streams, and lakes. Habitats with nearby timber and wetlands are preferred. Otters do not dig their own burrows and will often take over an abandoned beaver den. River otters will use abandoned muskrat or woodchuck burrows in areas without beaver dens.

Over the course of a year, a male river otter may use 40 to 100 linear miles of shoreline. Seasonally, a female river otter and her young will use relatively small sections of a waterway, typically three to ten linear miles. Females tend to have smaller home ranges than males.

Distribution and Abundance

At the time of European settlement, river otters were common throughout Illinois. Habitat loss, pollution, and unregulated hunting severely reduced the population. By 1989, biologists estimated that there were fewer than 100 river otters left in Illinois, and the river otter was added to the state endangered species list. In the mid-1990s, biologists with the Illinois Department of Natural Resources released 346 river otters from Louisiana in southeastern and central Illinois. River otter populations slowly increased, and in 1999, they were upgraded to a state threatened species. Further improvement in otter numbers allowed the river otter to be taken off the state threatened list in 2004. Today, the largest concentrations of river otters in Illinois are along the Mississippi River and its backwaters in northwestern Illinois. River otters are now a common species in Illinois and are found in every county. In some locations, river otter numbers have increased to such levels that they are sometimes considered a nuisance.

Reproduction

Young river otters (<i>Lontra canadensi</i>) often remain with the female until the following spring.
Photo courtesy of Robert Barber, Painet Inc. (IDNR image library)

River otters breed in late winter to early spring (January to April). The female carries the fertilized eggs for eight to twelve months before embryo development occurs (delayed implantation). Two to four kits are born two months later, arriving between January and May. The female raises the kits mostly without male assistance. Kits begin brief trips outside the den when they are 10 to 12 weeks old and take to the water when they are approximately 14 weeks. Young river otters must be taught to swim and are weaned by four months of age, but they often remain with the female until the following spring.

Food

River otters (<i>Lontra canadensis</i>) eat about 2 1/2 pounds of meat each day.  Illinois biologists have found remains of sunfish, carp, shad, bass, crayfish and frogs in otter scat. Otters will also eat salamanders, snails, clams, snakes, turtles, birds and insects. They often pull large fish onto shore to eat them.
Photo courtesy of Glenn Chambers (IDNR image library).

River otters feed mainly on fish and crayfish but will also consume frogs, salamanders, snakes, small turtles, aquatic invertebrates, earthworms, and carrion. They will pull large fish from the water so that they can feed on land, and they often leave uneaten fish parts on the shoreline. These signs can be used to help determine the presence of river otters in an area.

Behavior

River otters (<i>Lontra canadensis</i>) once were almost gone from Illinois. In 1994, the Illinois Department of Natural Resources began releasing otters and successfully restored them to the state's rivers and streams. 
Photo courtesy of Robert Barber, Painet Inc.(IDNR image library)

River otters are crepuscular animals (active around dawn and dusk). Males are typically solitary but occasionally spend time with family groups or with small groups of males. Females are usually accompanied by their young.

River otters are exceptional swimmers. Their body shape and broad tail help them to maneuver quickly in the water. They are capable of submerging for three to four minutes at a time and can swim a quarter of a mile underwater. River otters are very curious, playful animals. They are known to play with rocks and shells and to "slide" down steep banks. Occasionally, a curious river otter will approach a boat or a person standing motionless on the shore, in order to investigate the new object in their territory.

Longevity

Bobcats and coyotes are the main predator of river otters. Adults are able to defend themselves against most predators. If they survive the first year, river otters may live for eight to ten years.

Damage Prevention and Control Measures

River otters are not likely to cause problems in natural environments. Exclusion and removal are the best methods to remedy a fish depredation problem with river otters.

Habitat Modification

River otters do not build their own dens. Modifying the landscape by destroying beaver and muskrat lodges and burrows may discourage river otters from taking up residence on the property.

If otters are already present, adding aquatic vegetation or brush piles to ponds can provide fish with cover to help them escape river otters.

Exclusion

Fencing is an effective but often expensive technique to keep river otters out of an area. Water tanks or small ponds can be fenced with 3 x 3 inch mesh wire. Hi-tensile electric fences can also be effective. Four strands of wire should be placed at four to five inch intervals from the ground. Wires must be spaced closely enough that the otter cannot go underneath or between the wires without receiving a shock. Remove vegetation around the fence to prevent the electric charge from becoming grounded.

Repellents

There are no repellents registered for use on river otters in Illinois.

Removal

River otters that are causing property damage may be removed with permission from an Illinois Department of Natural Resources District Wildlife Biologist (DWB). Contact the local DWB to request an animal removal permit and instructions regarding the proper manner of capture and disposal. If the animal is to be removed using a livetrap, the trap must be at least 48 inches long. Wire live-traps used to capture raccoons and opossums are not long enough to trap river otters. It is usually best to hire an experienced Nuisance Wildlife Control Operator to remove river otters.

Public Health Concerns

River otters are not considered a public health concern in Illinois.

Ecological Role

River otters are a top aquatic predator. Their presence in a waterway indicates a healthy fish population.

Legal Status

River otters are legally protected by the Illinois Wildlife Code, but they can be trapped during river otter trapping season. If a river otter is causing property damage or is a public safety concern, it may be removed with the permisison of an Illinois Department of Natural Resources District Wildlife Biologist (DWB). It is usually easier to have river otters trapped by an experienced Nuisance Wildlife Control Operator.