The southern river otter, or South American river otter, is an otter species that lives in the southern regions of Argentina and Chile, including parts of Patagonia and Tierra del Fuego. It is listed by the International Union for Conservation of Nature as an endangered species.

Otters are carnivorous mammals in the subfamily Lutrinae. The 13 extant otter species are all semiaquatic, aquatic, or marine. Lutrinae is a branch of the Mustelidae family, which includes weasels, badgers, mink, and wolverines, among other animals.