About 100 species of mammals are endemic to the southeastern United States, an area of diverse habitat types and high biodiversity. Many of these species are either formally considered aquatic or semi-aquatic, or they are otherwise closely associated with aquatic ecosystems. In the southeastern United States, greater than 80 percent of mammalian species are listed in some category of concern throughout all or at least a portion of their ranges (i.e., endangered, threatened, under review for possible listing as endangered or threatened, species of special concern, species deemed in need of management, etc.). Almost all of these species are imperiled because their populations have declined to dangerously low levels due to habitat loss, habitat degradation, or other human-related factors. Most imperiled mammal taxa can be categorized as belonging to one of two general groups: habitat generalists or habitat specialists. Typically, habitat generalists have become imperiled mainly due to human exploitation, while habitat specialists have suffered primarily from habitat loss or habitat degradation.

The passage of the U.S. Endangered Species Act of 1973 resulted in an increased need for information concerning distribution and status of all native species. However, relatively little is known concerning the historical distribution and current status of many mammalian taxa, and this is particularly so for small non-game species. In this chapter we provide species accounts of mammals commonly associated with aquatic ecosystems that we consider to be imperiled in the southeastern United States. In these accounts we have included information which we feel is valuable toward best understanding the threats that challenge each considered taxon.