Despite its smaller size, the muskrat (Ondatra zibethica) can easily be mistaken for a beaver (Castor canadensis) or river otter (Lontra canadensis), as all are semi-aquatic mammals often seen in the water. Without a scale, all three look very similar while swimming with nose, eyes and ears streamlined with the surface of the water; make a note of its tail structure and swimming habits to help determine the species. Also note that the beaver and river otter are chiefly nocturnal and not often seen during the daytime.
The muskrat can easily be distinguished by its long, scaly, black tail which is slightly flattened from side to side and used propel itself through the water. In contrast, the beaver has a wide scaly tail which is flattened from top to bottom (shaped like a paddle) and is often heard slapping its tail against the water while diving. The river otter can appear somewhat playful in the water, diving often to catch fish, and is a more efficient swimmer with a long, thick and tapering, furred tail which is used in combination with its hind legs and semi-webbed feet in an undulating swimming motion. Like the otter, muskrats will dive beneath the surface to collect food such as aquatic vegetation as well as shellfish, frogs and sometimes fish.
Muskrats are slower swimmers and generally travel in direct lines to and from their 2-3ft tall conical houses made of marsh vegetation. Entrances to these houses are general sometimes underwater, so don’t be surprised if you see them dive beneath the surface several meters before reaching the shoreline.