There are the super, sexy headline-grabbers that people travel across the world to see, like polar bears and tigers and whales. And then there are the animals that you've always wanted to see, but never quite admitted it to yourself: smaller, more obscure, less charismatic, but which for some reason have a meaning for you.

I hadn't travelled across the world to see beavers. All the same, when I strolled up to see a beaver's pond, I felt an odd stirring of excitement. But it was only when I saw a big fat fellow waddling down to the pond with a large chunk of salad hanging negligently from his mouth that I realised I had always wanted to see a beaver.

I was in Canada, travelling with the tour company Wildlife Worldwide, and looking for something far bigger and sexier, a travel-across-the-world animal if ever there was one. But I forgot all about bears when I found myself face to face with a beaver. About twice the size I had expected, for some reason, and utterly unfazed by human company, he strolled at his ease down his own well-worn path and splashlessly entered his own well-swum pond.

Beavers are one of the few creatures - apart from human beings - that meticulously create their own environment. A beaver's estate is as unnatural a thing as a city: a place made, not begotten. A beaver's land is built, if not by the hand of Man, then certainly with the paw and tooth of beaver. The pond had been created by a dam, a massive piece of patient, heavy-duty engineering.

A second pond lay a few feet below it, linked by an underwater tunnel. And here was the beaver's lodge, an imposing structure that was like a stately home: something that had been improved and worked on, rethought and refaced by one generation of beavers after the next, the end result not so much the homogeneous product of a single mind as a continuous unfolding narrative.

Secret tunnels

The beaver sported himself in relaxed fashion, a beaver at home, utterly undismayed at this human company. I needed no binoculars, only an unassertive presence. Occasionally, he upended himself lazily, fat bum and big flat tail in the air, diving to find some agreeable piece of vegetation to chew on. For some herbivores, most of the known world is food, and the beaver had created his world for exactly this purpose.

A second, and younger, animal appeared on the lower pond, equally unworried by the visitors. It was behaviour that you normally see only at long range or when you have hidden for hours. It was an extraordinary thing - not to be hiding yet apparently invisible. Here was unearned privilege, watching beavers living out their lives while standing on their doorstep.

And then, for no reason that I could fathom, the bigger beaver upended with a sudden urgency, bashed his flat tail on the water with an echoing slap of warning and vanished; the smaller one took the hint and also disappeared, no doubt into the secret tunnels that led to the lodge.

So that was that: a long encounter with one of the most extraordinary mammals you could wish to meet. It was something of a return to childhood. I had always liked Mr and Mrs Beaver in The Chronicles of Narnia and, besides, the animal that builds dams and makes its own semi-submerged stately home was a must in all the Far Out children's guides to exploring Nature that I ever read.

To meet a couple in person, to walk by the dam, to see the lodge, confirmed that these strange stories of childhood are not fairytales but the sober truth. Not all the things that delight us as children are imaginary. The fabulous is not confined to fable, nor the fantastic to fantasy. The beaver's estate makes that very clear.

Back from extinction

And now we have beavers of our own. The European beaver was common in Britain until they were hunted to extinction, mainly because they make nice hats, in the 16th century. But they are being reintroduced - so far successfully in 24 European countries.

There have been a couple of small-scale, low-profile reintroductions in England as well over the past three years and, next year, four families will be reintroduced in Mid-Argyll, in Scotland.

It seems strange that an animal we consider an emblem of North America, most particularly of Canada, should also be a British animal, even if the two species are subtly different. We have no beavers in our fairytales, as we do with other lost British species such as wolves and bears.

But if the British beavers settle in and start breeding, they will do some big things. As engineers they will make ponds and create habitats for many other species. They are not animals that sit about. They need to be up and building stuff - stuff that lasts from generation to generation. If all goes well, beavers will reshape our land.

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