The highest populations of muskrat are in the broad floodplains and deltas of major rivers and in marshy areas dotted with small lakes. Their coats consist of soft, dense underfur and long, coarse, shining guard hairs. The guard hairs produce the dominant color of the upper parts.
Coloration ranges from a medium silvery brown to dark brown with a lighter belly.
The feet and tail are dark brown or black. In open, swampy areas muskrats construct houses of vegetation piled into mounds 2 to 3 feet above the surface of the water and 5 to 6 feet in diameter. They also tunnel into earth banks. Their nests are well above high water and have tunnels exiting underwater below the lowest freezing level. Muskrats construct slides and make fairly well-defined channels through vegetation along banks of streams and ponds.