Environmental experts are calling for water voles to be given full legal protection as figures suggest numbers have fallen by 95% in 20 years.
Water voles are one of the UK's most endangered species
They say the mammal, famously embodied by Ratty in Wind of the Willows, has disappeared from some areas and they blame the rise in mink predators.
The Environment Agency says full legal protection by the government is needed to prevent possible extinction.
But there are encouraging signs that voles are returning to some areas.
Evidence gathered by more than 6,000 people for British Waterways indicates voles are returning to breed in areas where special measures have been put in place.
The Kennet and Avon Canal near Bath and the Ashby Canal near Birmingham have seen water vole populations rise significantly as a result of conservation programmes.
But the overall trend is still worrying, said Alastair Driver, the agency's national conservation manager.
"Since 1990 the water vole population in Britain has been decimated, with 95% of their numbers wiped out.
"Full legal protection has been on the agenda for over a decade, but we can't wait any longer.
"Without direct action the wild water vole population will decline beyond the point of no return over much of its range within 10 years."
The Royal Society for the Protection of Birds fears for the species
The Wildlife and Countryside Act 1981 gives the mammal's habitat "limited" legal protection but the water vole itself is not protected.
The agency said protection would mean any developer wanting to build near its habitat would have to act to ensure there was no impact on the creatures.
It is now trying to raise awareness among communities about the species by publishing a handbook containing details of the best conservation methods based on the latest science.
Dr Tom Moorhouse, from the Wildlife Conservation Research Unit, said the vole's long-term survival required "a twin-track approach that diminishes the threats to existing populations and encourages the species to recover in areas where it has become virtually extinct".
The news comes as The Royal Society for the Protection of Birds (RSPB) claims the government's Environmental Liability Directive will exclude 375 of the UK's "priority species", including water voles, scarce farmland birds, red squirrels and 2,400 Sites of Special Scientific Interest (SSSI).