The Southwestern Water Vole, Arvicola sapidus, occurs only in freshwater habitats in parts of France, Spain and Portugal, where it is found from sea level to a maximum of about 2,300 m in the Pyrenees (Le Louarn and Quéré, 2003).

In France, the water vole remains relatively common in only three regions: Charente-Maritime, Brittany and southwest France (Pyrenees), though its distribution is still patchy in these areas. In the French départements of Drôme, Var, Alpes-Maritimes, Hautes-Alpes, Alpes-de-Haute-Provence, Loire, Rhône and Ain, the water vole has become rare, with a maximum of only 10 locations per département. In the Ain there is only one location, two in the Rhône and no more than 6 or 7 in the Hautes-Alpes.

In Spain, the water vole is now restricted to the northern and eastern parts of the country, and has disappeared from central Spain, where it was formerly common.

Locations of the water vole in Portugal are not well-documented but, as in other parts of its range, the water vole seems to be restricted to fairly isolated subpopulations in only a few parts of the country.