This weekend marks one year since beavers were released into the wild in Scotland for the first time since the 17th century.

The reintroduction of the animals to Knapdale Forest in Argyll has been controversial as our Scotland Correspondent, James Cook explains.

True to form the beavers have been busy.

After a 400 year absence from Britain they wasted no time in getting to work.

In a dappled clearing of Knapdale Forest the evidence of their activity is all around.

Sharp teeth marks are left on several large trees which have been gnawed to the ground as timber.

A little deeper into the woodland, a small clump of rowan trees has been felled and dragged away.

Sharp twigs

In fact the beavers have neatly thinned out a whole section of the forest near Barnluasgan.

The little lumberjacks have removed the wood for a major construction project - a dam built with remarkable precision.

It's an impressive piece of engineering. Earth, moss and wood are propped up by a neat array of sharp twigs, supported by larger logs which even a human would find difficult to lift.

Image caption Nick Purdy calls the beavers the "natural woodland managers"

All but a trickle of water has been stopped, flooding the flat land upstream, including a forestry path.

The result has been to extend the beavers' territory, giving them more shallow water in which to forage, seek shelter and, possibly, breed.

Nick Purdy who manages the area for the Forestry Commission is impressed with what he calls the "natural woodland managers".

He explained: "Dare I say it, some of our forestry contractors have probably got something to learn from them

"They've been felling material for creating the dam and it's all cut to length, it was all presented perfectly for dragging out to the dam.

"You'd have thought people were doing it rather than beavers to be honest."

Chubby spaniels

All this work was carried out by animals which are not much bigger than chubby spaniels.

As dusk fell earlier this week a small group of enthusiasts watched as one beaver emerged from the family lodge.

The animal glided silently across the water, pushing out a little bow wave before dipping and diving with a flash of a powerful tail.

The first 12 months of this five year trial have seen their ups and downs.

Image caption Evidence left by the beavers handy work

But the Royal Zoological Society of Scotland and the Scottish Wildlife Trust which are running the project, insist it's been a success so far.

Simon Jones, project manager of the Scottish Beaver Trial, said: "We're really happy with the way things have gone to date.

"So far we've released four families of animals into the wild here at Knapdale.

"Three of them have settled really well and have gone on to build lodges to show that they've settled in."

The fate of the fourth family is murkier. Three beavers disappeared last August after reports of unauthorised shooting in the trial area.

The beaver reintroduction has plenty of opponents in Argyll and there was speculation that the animals had been shot or scared off by the gunfire.

Both are possible, admits Mr Jones, but he says an investigation into the disappearance and the gunshots was inconclusive.

"It may have been a sheer coincidence," he says.

Beavers have to cut down trees on a regular basis to eat Jane Allan

The episode did highlight the opposition of some locals, particularly anglers, to the experiment.

Two miles downstream from the beavers at Barnluasgan is Seafield Farm where Jane Allan manages holiday cottages and makes baskets.

She said: "We have concerns about the beavers long term because we're worried that they will create such a huge impact on the environment."

Mrs Allan added that three beavers have turned a "fairly small marshy puddle" into a little loch and she thinks such change will continue.

She pointed out: "Beavers have to cut down trees on a regular basis to eat.

"They have to eat a huge amount of vegetable matter to keep themselves going and if you look at any of the places that the beavers have been they have created quite a lot of devastation."

While the project team insist they are listening to such concerns, the next stage of the trial may upset the critics even more.

Conservationists are hopeful that the animals will now breed.

Scotland's first baby beavers in four centuries would not be welcomed by all.