There are two subspecies of the water vole: Arvicola sapidus sapidus (Miller, 1908) and Arvicola sapidus tenebricus (Miller, 1908). A. s. sapidus is present in Portugal and southern Spain, while A. s. tenebricus occurs in France and northern Spain. A. s. tenebricus is dark to reddish brown, while the coat of A. s. sapidus is generally lighter and more yellowish.

The Southern Water Vole is endemic to Europe, where it is restricted to Portugal, Spain and France, and is declining in most parts of its range. It is listed as Near Threatened (approaching Criteria A2ace) because this species has undergone a suspected reduction in both the number of individuals and sub-populations throughout its range. The rate of decline is not well documented, but given decline rates recorded in parts of its distribution as well as ongoing habitat modifications and competition with invasive species, it is likely that the decline has reached between 20-25% over the previous ten years. Whilst the situation is somewhat less clear in Portugal, the species is experiencing similar threats there, and it is inferred that similar patterns of reduction have likely occurred. Research is urgently needed to improve knowledge of this species' status and trends.

The European endemic Southern Water Vole (Arvicola sapidus) is restricted to freshwater habitats in mainland parts of France, Spain and Portugal. It is found from sea level to a maximum of about 2,825 m (Krystufek and Shenbrot 2022).

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 six or seven in the Hautes-Alpes.

In Spain, the water vole is distributed with a certain continuity in the northern and eastern parts of the country, while in the rest of the country it becomes more localised and in some parts has become scarce or even disappeared (Central Spain) (Ventura 2017, Román 2020).

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.

The Southern Water Vole is declining in most parts of its range. Experts suspect that it has declined by 20-25% across its global range over the previous decade (G. Amori pers. comm. 2024; L.J. Palomo pers. comm. 2024). In France it is much less common than it was 10–15 years ago (S. Aulagnier 2006), and in the Iberian Peninsula it is considered to be declining as a result of habitat loss and degradation (Palomo and Gisbert 2002), although it is not currently classified as threatened in Portugal (Cabral 2005, Bencatel et al. 2019). Several studies have shown that, in optimal habitat, water vole density can reach five individuals per 100 m of river bank, but that it is unlikely to exceed this figure (Saucy 1999, Palomo and Gisbert 2002). Population fluctuations are not known (Saucy 1999).

France
A recurring problem with accurately determining the full extent of water vole population decline is that the species has been poorly documented in the past, with older information on water vole populations being anecdotal and patchy. For example, an atlas of mammals of France (1984, Société Française de l'Etude et Protection des Mammifères - SFEPM) mentioned no threat to the water vole, and reported a nationwide distribution of the species, with the exception of Corsica, the North, North-East and the Alps. There were no national surveys on the Southern Water Vole and the vole was not even mentioned in the Action Programme for wild fauna and flora, a wide-ranging survey published in 1996 by the French Ministry for the Environment. In contrast, over the last 10 years, there has been increasing attention on the water vole, mainly due to its apparent disappearance from many areas, a great cause for concern in a species with a normally high reproductive potential (three to four litters per year, averaging 3.5 young per litter). Observation data reported on the French Red List indicates a concerning decline since at least 2018, and the species is categorised as Near Threatened there (MNHN and OFB 2024).

Spain
The water vole has previously been little known and studied in Spain, yet its numbers have probably suffered drastic declines in recent years, making it crucial to carry out further research and monitoring of the species (J. Román pers. comm., 2007). Experts in Spain seem to agree that the Southern Water Vole is facing similar threats in the Iberian Peninsula as those in France (M. Delibes pers. comm. 2007). The water vole is not currently classified as a threatened species in any part of its range in the Iberian Peninsula, yet its subpopulations in this region exhibit a marked reduction, due to human-induced habitat degradation, destruction or modification, such as cementing over of riverbanks, canal-building, destruction of vegetation along waterways, draining of wetlands and water pollution (Álvarez et al. 1985, Garde 1992). In 2011-2012 surveys of Arvicola sapidus, the species was detected in 34.9% of 2,914 sampled points in Spain, and it was considered scarce in multiple regions including coastal areas, dry areas of Ebro Valley, and several mountain systems (the Pyrenees, the Central System and the Cantabrian Mountains) (Román 2020); there are plans to repeat this census in 2024-2025 (L.J. Palomo pers. comm. 2024).

Portugal
The water vole faces a similar situation in Portugal to that confronting its subpopulations in France and Spain, though its status in this country is perhaps the least well-documented of the three. Research conducted in several locations in Portugal where the Southern Water Vole is present leads to the conclusion that it is scarce and under threat principally from habitat disturbance and predation, as well as isolation of subpopulations owing to the scattered nature of suitable habitat in Portugal. A recent study in the southwest of Portugal has confirmed the species’ presence, although at low densities (Sabino-Marques et al. 2018). The Portuguese Mammal Atlas shows its distribution as sparse, but it is not known whether this is because the species genuinely has a restricted distribution, or whether this is reflective of a low survey effort (Bencatel et al. 2019).

The water vole is almost always found near water, preferring small (under eight hectares) freshwater lakes, ponds and slow-moving rivers and streams with dense riparian vegetation (Saucy 1999, Fedriani et al. 2002). It sometimes occurs in drainage ditches and wet fields. Abundant hydrophilic vegetation and shorelines suitable for water vole burrowing activity seem to be essential characteristics of water vole habitat. Suitable habitat for the species had high cover of herbaceous plants (mainly helophytes) and moderate to low tree and shrub cover (Mate et al. 2013). Its diet consists mainly of aquatic plants, grasses, and herbs, although small animal prey are occasionally taken (insects, fish, tadpoles, freshwater shrimp). The burrows of the water vole typically have two entrances - one primary entrance above water level and one underwater entrance. The water vole is mainly active during the day, with two peaks in activity in late morning and early afternoon, as well as some nocturnal activity. It is active throughout the year, with no period of hibernation.

Reproduction occurs between March and October, with three to four litters of two to eight young per litter, with the average reported as 3.5–6 young. The gestation period is three weeks. Sexual maturity is reached at five weeks old and the life span of the water vole varies from two to four years. The water vole lives in small family groups and, under optimal conditions, its density may reach five individuals for every 100 meters of riverbank (Saucy 1999, Palomo and Gisbert 2002). There have never been any records of damage to human activity or agriculture by the water vole.

Home ranges and distance travelled have been shown to be larger in sections of better quality habitat, and smaller in poorer quality habitat, whilst population density has been shown to be higher in better quality habitat (Mate et al. 2016). The home ranges of individuals also changed with the emergence of new available gaps and in response to reproduction needs. Adult males are not thought to interact within groups, while male and female adult interactions intensified during reproductive periods (Mate et al. 2016).

Since the Southern Water Vole is restricted to wetland areas, it faces all the usual threats associated with this habitat. The Southern Water Vole only flourishes where the banks and vegetation have not been significantly altered by human activity. Consequently, habitat loss and degradation (as a result of drainage, dredging, canal-building, infrastructure development, intensive agriculture and droughts) are major threats. Competition with the introduced Coypu (Myocastor coypus) and Muskrat (Ondatra zibethicus) for food and dens is also a threat. In Spain, water vole decline is attributed primarily to anthropogenic habitat modification, but competition from the Norway Rat (Rattus norvegicus) may be an additional factor threatening the Southern Water Vole (Palomo and Gisbert 2002). Efforts to control invasive species by poisoning have resulted in accidental water vole deaths.

Despite the threats posed by agriculture to the species, it is possible that irrigated ditches and vegetated areas of farmland can facilitate the dispersal of water voles (Pita et al. 2013).

In Spain, the Southern Water Vole is considered a delicacy and is still consumed occasionally despite this practice being illegal.

The Southern Water Vole occurs in some protected areas within its range, although this does not particularly improve the status of this species. As yet, the water vole receives no legal protection under EU legislation (Cabral 2005), nor national legislation in any of the three countries where it occurs. However, in the Spanish red book, it has been classified as Vulnerable VU A2ace+3ce (cf. Romàn 2007) and is listed as Near Threatened on the French Red List (MNHN and OFB 2024). Further research is urgently needed to monitor the population trend, and the aquatic habitats where the water vole occurs require protection.

Nature et Humanisme and the SFEPM recommend the following methods for protecting the water vole (J.F. Noblet pers. comm.):

• Prevention of the use of rodenticides in the habitats occupied by the Southern Water Vole.
• Alternative methods of combating the proliferation of the Muskrat, Coypu and American Mink, by more selective means (live cage traps, etc.).
• Forbidding the raising, import, transport or release of these three animals.
• Legislative protection of the water vole, under Annexes I or II of the EU Habitats Directive, the Bern Convention, as well as in national legislation, and legislative protection of the water vole's habitat.
• Information campaigns directed at the concerned parties (local elected officials, waterway engineers, waterway management bodies, etc.).
• Regulation of management techniques of waterways and their shores, such as forbidding dredging and paving of water vole habitat and destruction of riverside vegetation.
• Forbidding destructive agricultural practices and associated water pollution.
• International cooperation between France, Spain and Portugal in protecting the Southern Water Vole and coordinating research in cross-border areas where the water vole may occur.
• An ongoing research programme, in order to thoroughly map and monitor the remnant populations and their trends and to analyse the reasons for their ongoing decline.
• A captive breeding programme and eventual reintroduction of the Southern Water Vole in suitable protected habitat.