There are about five young in a litter, which are born below ground in a nest made from suitable vegetation, notably grasses and rushes. Although blind and hairless at birth, young water voles grow quickly, and are weaned at 14 days. On average, water voles only live about five months in the wild. On the continent they behave quite differently, living away from open water and are regarded as serious agricultural pests. In Britain, water voles occasionally undermine river banks, but otherwise they are harmless and cause no damage.
Recent evidence suggests that water voles have undergone a long term decline in Britain.
Predation by the introduced American mink is thought to have a severe impact on water vole populations, even causing local extinctions. This may be because their usual way of evading predators, by diving and using burrows with underwater entrances, does not protect water voles from the mink. Removal of mink is unrealistic for large areas but can be carried out locally in nature reserves and along key sections of rivers to protect remaining water vole populations. Habitat degradation and pollution are also thought to have contributed to the decline of the water vole. Riverside works such as dredging and clearance of bankside vegetation removes large amounts of the plants water voles depend on for food and causes disturbance.