You do not need the skills of a Native American tracker to spot the telltale signs that a beaver is on the loose in Devon. Even a shortsighted hack in a woolly hat could find them.

The first clue was a tree stump three feet wide that looked as if it had been gnawed by a giant rodent. That was the second thought that went though Philip Kelly’s head when he stumbled across it while checking reports of a precariously leaning tree near a pumping station on the River Tamar.

The South West Water worker said: “My first thought was children messing about with an axe, but then I looked around and saw other trees and branches had also been gnawed and I said to my mate, ‘There’s a beaver been at work here’.”

A few minutes’ research led him to Derek Gow, a conservationist who keeps beavers at a farm less than 20 miles away. Three of Mr Gow’s prize specimens had escaped four weeks earlier. Two had been recaptured but the third, a large male weighing 40kg (6st 4lb), was still at large. Mr Gow pointed out other signs that we had found his missing beaver: the prints of webbed feet in soft mud, a slide down the river bank where branches had been dragged, chippings as neat as though they had been chiselled beneath comically sharpened stumps.

However, contrary to claims that this is a trail of destruction, Mr Gow sees it as a work in progress. Not for nothing have beavers given their name to industrious, unremitting labour. The beaver helped to shape the British landscape and the environment in which many of our best-loved species thrived, from the brown trout to otters, water voles and myriad species of insect.

We tracked the creature’s toothy progress through the undergrowth, alongside a tiny feeder stream and there, on the opposite bank, we spotted the first beaver’s lodge to be built outside a wildlife park for centuries. Beneath the trunk of a fallen tree was a stack of smaller branches, neatly wedged to both conceal the underwater entrance to its burrow and provide a fresh supply of crunchy snacks within easy reach.

Mr Gow’s beaver was imported from Bavaria: the winters there are harsher than in Devon, where it was a mere minus 1C (30F). He said: “It’s laying up a store of feed because it doesn’t know it isn’t in Germany.”

The beaver’s freedom will last only as long as it takes to build some incisor-proof traps. But for other beavers the Devon countryside is beckoning. South West Water believes that the rodents could make a significant contribution to water conservation.

Martin Ross, the company’s environment manager, is hoping to release between 40 and 50 into water courses in Devon and Cornwall. By literally beavering away building little dams, the creatures will create a filtration system with the potential to remove silt and pollutants that would otherwise need expensive treatment. He said: “We have been looking at other places in Europe where this has been tried and the results are remarkable. Beavers work for free and do a job that would otherwise require large and expensive treatment plants.”

History does not record who first discovered that the viscous yellow liquid contained in two large glands in a beaver’s bottom helped to cure headaches, but it is one of many reasons why, by the start of the 20th century, they had been hunted nearly to extinction across most of Europe. The last documented evidence of beavers in England is an entry in a parish register of 1789, when a Yorkshire farmer was paid 2d (1p) for a beaver’s head under the Elizabethan vermin laws.

Mr Gow said: “It is not a question of whether they will be reintroduced into the wild in Britain, but when.

“To compare them to the introduction of mink or the grey squirrel as some have done is completely misguided. It is with very good reason that Native Americans called the beaver ‘nature’s kidneys’.”

Times recommends

• Energy-saving ideas from switched-on professor
• Rooks are as clever with tools as chimpanzees
• Burping of the lambs blows roast off menu