The UK's fastest declining mammal has been brought back to the River Ver after a 34-year absence.

On Tuesday, Herts and Middlesex Wildlife Trust, in partnership with the Ver Valley Society and a number of private landowners, reintroduced the nation’s water vole to a stretch of the River Ver to the west of St Albans.

The reintroduction was made possible by funding from the Debs Foundation and Linder Foundation.

Water voles were once abundant in rivers throughout Herts, but populations have declined by over 90 per cent in the last 50 years due to a combination of habitat loss and because they are being killed and eaten by American mink, an invasive, non-native species.

Increases in the population have only been noted in recent years where habitats have been improved or through carefully planned introduction programmes.

Herts and Middlesex Wildlife Trust is aiming to have thriving populations of water voles back in every river in the county by 2030.

Specialist breeders brought the 150 water voles from Devon to a stretch of the River Ver to be released. Prior to this reintroduction, the last recorded sighting of a water vole on the River Ver was in 1987.

Herts Advertiser: Water voles have been released into the River Ver.Water voles have been released into the River Ver. (Image: Giampaolo Masserano)

Conservation officer Josh Kalms said: “We are thrilled to have reintroduced water voles to the River Ver. Water voles are a key species in wetland ecosystems and their actions are important for maintaining healthy wetland ecosystems – they are mini ecosystem engineers with their burrowing and feeding helping our river banks and wetlands stay in good condition."

Herts Advertiser: Water voles have been released into the River Ver.Water voles have been released into the River Ver. (Image: Herts Wildlife Trust)

Volunteers transported the voles in pairs to pens set out along the river bank so they have time to settle into their new environment.

Herts Advertiser: Volunteers release water voles into the River Ver.Volunteers release water voles into the River Ver. (Image: Herts Wildlife Trust)

After a few days of supplementary feeding with fruits and vegetables, the pens are removed and the voles will make their own burrows below the water’s surface. A few solitary voles will also be released directly onto the river bank.

Herts Advertiser: Volunteers release water voles into the River Ver.Volunteers release water voles into the River Ver. (Image: Herts Wildlife Trust)

Chairman of the Ver Valley Society John Pritchard said: “The society is delighted to have been involved in this wonderful initiative. We have long been campaigning for the return of the River Ver’s former flow and wildlife and the reintroduction of water voles is one of the highlights of that journey.

Herts Advertiser: Volunteers release voles into the River Ver.Volunteers release voles into the River Ver. (Image: Herts Wildlife Trust)

"Over 40 volunteers have enjoyed every minute from the initial planning a number of years ago, to installing the pens and daily checks before finally opening the doors to see the voles go free.”