A water vole's usual escape is to dive and enter a bank burrow whose entrance is too narrow for a fox or an otter. American mink, established in Britain from fur-farm escapes and releases from the 1950s onward, broke that defence: female mink are slender enough to pursue voles into the burrow system itself.
The scale of the loss was documented by national surveys in the 1990s, which found the species missing from the great majority of previously occupied sites. Habitat degradation, bank engineering and fragmentation had already reduced and isolated colonies, so mink predation acted on populations with little capacity to recolonise.
The global status misleads if read alone. Arvicola amphibius is Least Concern across its Eurasian range, but it is a conservation priority in Britain, where recovery work now combines catchment-scale mink control with bank habitat restoration and, in some catchments, reintroduction. The vole is also routinely mistaken for a brown rat; the blunt muzzle, small hidden ears and furred tail distinguish it.