Video report by ITV News Correspondent Angus Walker
About 100 water voles are being released in the Yorkshire Dales by the National Trust.
The endangered mammals are being returned to Malham Tarn in what is thought to be the highest reintroduction project for the endangered mammal in Britain.
The National Trust said it will be the first time the rodents have been seen there in 50 years.
The water vole - which is still best known as the inspiration for the character Ratty in Kenneth Grahame's Wind In The Willows - is Britain's fastest declining wild mammal.
National Trust ecologists believe Malham Tarn's water voles were wiped out in the 1960s by mink, which escaped from nearby fur farms.
The animals, which have been bred in captivity, will be released in the fen area of the tarn this year, with a further 100 voles due to be released in June 2017.
Here are some facts from the National Trust about water voles:
They measure around 12in (31cm) in length (8in/20cm body, 4in/11cm tail) and weigh between 200g and 350g - about the same as a half-size tin of baked beans
They live in burrows dug into banks along slow-moving rivers, streams, ditches and in wetlands
They are predominantly herbivores, eating grass and other waterside vegetation
A water vole will consume around 80% of its body weight in food every day