Historical records indicate that river otters were well established throughout most major drainages in the continental United States and Canada prior to European settlement (Hall 1981). The continent’s largest otter populations occurred in areas with an abundance and diversity of aquatic habitats such as coastal marshes, the Great Lakes region, and glaciated areas of New England (Nilsson 1980; Toweill and Tabor 1982; Melquist and Dronkert 1987). In addition, riverine habitats in interior regions supported smaller, but viable, otter populations (Nilsson 1980).

North American river otters prefer bog lakes with banked shores containing semi-aquatic mammal burrows and lakes with beaver (Castor canadensis) lodges, and they avoid water bodies with gradually sloping shorelines of sand or gravel (Reid et al. 1994b). In Maine, use of watersheds by river otters is negatively associated with the proportion of mixed hardwood-softwood stands in forested areas adjacent to waterways and positively associated with the number of beaver flowages, watershed length, and average shoreline diversity (Dubuc et al. 1990). In Idaho, river otters prefer valley over mountain habitats, and they select valley streams over valley lakes, reservoirs, and ponds (Melquist and Hornocker 1983). Logjams are used intensively where present (Melquist and Hornocker 1983). In Florida, abundance of North American river otters is lowest in freshwater marshes, intermediate in salt marshes, and highest in swamp forest. During the dry season, L. canadensis will retreat from marshland and move to permanent ponds where water is available and food is more concentrated (Humphrey and Zinn 1982). In Idaho and Massachusetts, habitat features preferred for latrine sites include large conifers, points of land, beaver bank dens and lodges, isthmuses, mouths of permanent streams, or any object that protrudes from the water (Melquist and Hornocker 1983; Newman and Griffin 1994).

The diet of the North American river otter is comprised mostly of fish that are abundant, midsized, and close to shore (Larsen 1984; Stenson et al. 1984), as well as amphibians (mostly frogs) and crustaceans (mainly crayfish) (Knudsen and Hale 1968; Reid et al. 1994a; Sheldon and Toll 1964). Small mammals, mollusks, reptiles, birds, and fruits are consumed opportunistically (Gilbert and Nancekivell 1982; Greer 1955; Hamilton 1961; Morejohn 1969; Verbeek and Morgan 1978; Wilson 1954). North American river otters have few natural predators in the water: alligators (Alligator mississippiensis), American crocodiles (Crocodylus acutus), and killer whales (Orcinus orca). They are considerably more vulnerable on land or ice where bobcats (Lynx rufus), cougars (Felis concolor), coyotes (Canis latrans), dogs (Canis familiaris) and wolves (Canis lupus) can kill adults (Melquist and Dronkert 1987; Melquist and Hornocker 1983; Route and Peterson 1991; Toweill and Tabor 1982). Most mortality, however, is human-related and includes trapping, illegal shooting, road kills, and accidental captures in fish nets or set lines (Jackson 1961; Melquist and Hornocker 1983).

North American river otters can reach 13 years of age in the wild and up to 25 years of age in captivity (Melquist and Dronkert 1987; Stephenson 1977). Females usually do not reproduce until 2 years of age, although yearlings occasionally produce young (Docktor et al. 1987; Hamilton and Eadie 1964). Males are sexually mature at 2 years of age (Hamilton and Eadie 1964). North American river otters usually breed from December to April (Hamilton and Eadie 1964; Liers 1951), gestation lasts 61-63 days, and young are born between February and April (Hamilton and Eadie 1964; Melquist and Hornocker 1983). Litter size may reach five (Park 1971) but usually ranges from one to three (Docktor et al. 1987; Hamilton and Eadie 1964; Tabor and Wight 1977).