New colonies of water voles, the UK’s fastest-declining mammal, have been discovered in the uplands of south Wales, offering hope for their survival.

Traditionally found along riverbanks, water voles have now established habitats in the valleys, which could help prevent their local extinction.

Robert Parry, chief executive of the Initiative for Nature Conservation Cymru (INCC), called the discovery “huge.”

Speaking to BBC Radio Wales Breakfast, he said: “We didn’t know they were up there, they’re on the verge of extinction, we’ve been looking for them for decades.”

The INCC-led project, funded by the Pen y Cymoedd Community Fund, surveyed ditches, marshes, and peat bogs across the Rhondda and Afan valleys from May 2024. So far, 20 new water vole colonies have been identified, making these uplands a crucial refuge for the species.

Once widespread in Wales, water voles have suffered a dramatic decline due to habitat loss and predation by the invasive American mink, which can wipe out entire colonies in days. However, upland areas, where mink are less common, provide safer environments for the rodents.

Conservationists report a 90% population decline over the past 30 years. INCC conservation officer Eliza Chapman expressed hope that the species’ expansion into uplands would prevent local extinction.

In recent years, over 40 water vole colonies have been recorded, highlighting their importance in maintaining upland ecosystem health. These semi-aquatic rodents, sometimes called “water rats,” play a key role in wetland biodiversity, demonstrating the significance of ongoing conservation efforts in Wales.