Britain’s endangered water voles will reach new heights when they are returned to Yorkshire’s Malham tarn for the first time in 50 years.

Around 100 water voles will be reintroduced on Friday to the National Trust estate in the Yorkshire dales, home to England’s highest freshwater lake, in what the trust says is the highest-altitude reintroduction of the species it has carried out in Britain.

Immortalised as Ratty in Kenneth Grahame’s The Wind in the Willows, the water vole is Britain’s fastest-declining mammal. The animal was once found in nearly every waterway in England, Scotland and Wales, but is now thought to have been lost in up to 90% of these sites, clinging on in isolated pockets, coastal marshes and backwaters.

The intensification of agriculture, pollution and development, plus poor riverside management, has brought about the loss and degradation of the riverbank habitat in which the voles live. But the sharpest declines in the past 30 years have been caused by the spread of the American mink. These animals have established themselves on the waterways after escaping from fur farms, and they prey voraciously on the water vole.

The water voles being transported to Malham tarn ahead of their release. Photograph: Richard Rayner/North News & Pictures Ltd for National Trust

Reintroduction schemes, alongside programmes to control mink and manage habitats, are providing a lifeline for the species. Water voles have recently been returned to Cornwall after being declared extinct in the county, to the South Downs national park and to Gwent in south Wales.

The Malham voles have been bred in captivity by a specialist agency and will be released over five days into the fen area of the tarn, which is unique for its flora, fauna and geology. A glacial lake set among ancient limestone pastures and upland hill farms, it is home to rare plants and animals including stonewort, sheltering pea mussels and the three-spined stickleback. The tarn also provides food for diving birds such as great crested grebes.



At 377 metres above sea level, it is England’s highest freshwater lake, and this is the highest-altitude release undertaken by the National Trust. Previous upland releases have taken place at Duchray in the Scottish Highlands (up to 300m) and Brecon Beacons in Wales (154m).

It is hoped the animals will recolonise the tarn and its surrounding streams, and play an important part in the ecosystem, grazing and burrowing into areas of the riverbank and allowing rare plants to grow, including mosses and liverworts that need patches of open habitat. The water voles will also act as a food source for predators such as barn owls and otters.



Roisin Black, a National Trust ranger at Malham tarn, said: “In the rest of Europe, water voles are common. In Britain, the creatures are incredibly rare. We know water voles have thrived at Malham tarn in the past and, thanks to work by the National Trust, the habitat here is perfect for water voles again.”



The animals will spend two days in large cages on the fringes of their new home. On the third day, the doors will be opened, with food placed on rafts in the water to encourage the voles to leave the cages and burrow in the banks. After five days, the cages will be removed altogether.



Rangers will monitor the health of the population, with a view to releasing a further 100 water voles in June next year.

The reintroduction is part of a new land management approach agreed in 2015 for the 8,000 hectares of National Trust land in the Yorkshire dales. Farmers and partners will work with ecological processes to create a landscape that looks like the traditional dales but has a wider variety of natural habitats – moors, fields and woodlands – and better connections between them.



Peter Welsh, ecologist for the National Trust in the Yorkshire dales, said: “Water voles once played an important part in the ecosystem at Malham tarn. Reintroducing them to the tarn is just one of the ways we are working alongside our farmers and other partners to restore wildlife and natural processes in the Yorkshire dales landscapes we care for.”