- Video report by ITV News Anglia's Liz Summers
The re-introduction of water voles to a site near Bishops Stortford three years ago has been a success, according to conservationists.
The Wildlife Trust moved almost 200 creatures to Thorley Wash following plans to flood their territory, and surveys suggest the population is now thriving.
Water voles are the UK's fastest declining mammal, with habitat loss and water pollution among the contributing factors.
"They've certainly been found three or four kilometers up towards Bishop's Stortford and five or six kilometers down towards Sawbridgeworth so we know that they're doing well here," Martin Ketcher from the Wildlife Trust told ITV News Anglia.
"We know they're spreading up and down the river."