Bank dens are common and these usually have underwater entrances leading upwards to hollowed out chambers in the bank above the waterline. Trails of air bubbles can often be seen through thin ice. These bubble trails are made by muskrats exhaling air as they swim beneath the frozen surface. General Uncontrolled muskrat populations do cause damage to private property and habitat. Hole digging activities undermine earthen dams and dikes.
Damages also occur to irrigation canals and farm ponds.
These areas are simply overcropped by the feeding activities of the muskrats and the loss of vegetation and resulting silting makes the area less productive for other wildlife species as well. Muskrats are an important prey for a variety of wildlife, including mink, fox, coyotes, hawks and owls. One major disease is Errington's disease. This serious virus can live in mud and infect muskrats in areas that have been uninhabited by other muskrats for as long as 5 years. Epidemics can and do occur with this devastating disease.