Threats to otter populations in North America vary among regions and are influenced by type, distribution, and density of aquatic habitats and characteristics of human activities. Prior to settlement of North America by Europeans, otters were widespread among aquatic habitats throughout most of the continent (Hall 1981). Unregulated trapping and loss or degradation of aquatic habitats through filling of wetlands and development of coal, oil, gas, tanning, timber, and other industries resulted in extirpations or declines in otter populations in many areas (Toweill and Tabor 1982, Melquist and Dronkert 1987). Nilsson (1980) reviewed the status of otters in the United States and determined that populations were extirpated in 11 states and had experienced severe declines in 9 other states. The most severe population declines occurred in interior regions where fewer aquatic habitats supported smaller fewer otter populations. Although the distribution of otters became reduced in some regions of southern Canada, the only province-wide extirpation occurred on Prince Edward Island (Polechla 1990).

During the 1970’s, improvements in natural resource management techniques coincided with increased concern about otter declines in North America (Endangered Species Scientific Authority 1978). Consequently, many wildlife management agencies developed strategies to restore or enhance otter populations, including the use of reintroduction projects (Ralls 1990; Serfass et al. 1993). Since 1976 over 4,000 otters have been reintroduced among 21 states. Also, 29 states and all Canadian provinces except Prince Edward Island have viable populations that sustain annual harvests. Annual harvest numbers of Northern river otters are similar for Canada and the United States (Obbard 1987), with most pelts being used in the garment industry (Toweill and Tabor, 1982). In the late 1970s, annual harvest in North America reached ca. 50,000 pelts, for a value of U.S. $3 million (Melquist and Dronkert, 1987). Otters are incidentally harvested by traps set for beavers (Toweill and Tabor, 1982), and therefore management plans should consider both species simultaneously (Polechla, 1990). While current harvest strategies do not pose a threat to maintaining otter populations, harvest may limit expansion of otter populations in some areas (Lariviere and Walton 1998).

Oil spills present a localized threat to otter populations, especially in coastal areas. Water pollution and other degradation of aquatic and wetland habitats may limit distribution of otters and pose long-term threats if enforcement of water quality standards are not maintained and enforced. Acid drainage from coal mines is a persistent water quality problem in some areas that eliminates otter prey prevents thereby inhibits recolonization or expansion of otter populations. Recently, there has been discussion of the long-term genetic consequences of reintroduction projects on remnant otter populations (Serfass et al. 1998). Similarly, many perceived threats to otters such as pollution and habitat alterations have not been rigorously evaluated.
The threat of disease to wild otter populations is poorly understood and has received little study (Serfass et al. 1995). Lontra canadensis may be victim of canine distemper (Harris 1968; Park 1971), rabies (Serfass et al. 1995), respiratory tract disease, and urinary infection (Hoover et al. 1984; Route and Peterson 1991). In addition, North American river otters can contract jaundice, hepatitis, feline panleucopenia, and pneumonia (Harris, 1968). North American river otters host numerous endoparasites such as nematodes (Hoberg et al. 1997), cestodes (Greer 1955), trematodes (Hoover et al. 1984), the sporozoan Isopora (Hoover et al. 1984), and acanthocephalans (Hoberg et al. 1997; Hoover et al. 1984). Ectoparasites include ticks (Eley 1977; Serfass et al. 1992), sucking lice Latagophthirus rauschi (Kim and Emerson 1974), and the flea Oropsylla arctomys (Serfass et al. 1992).