THEY used to be a familiar sight in almost every river across the country.

Beavers and their cleverly constructed dams were an integral part of Britain's waterways before the nocturnal creatures were hunted almost to extinction in the 16th century.

Europe's largest rodent has now been absent from the English countryside for more than 400 years.

However, they are poised to make a comeback under proposals to re-introduce the species in Scotland and possibly other parts of the UK, including the New Forest.

About 20 beavers from Norway are due to be released into the wild by the Scottish Wildlife Trust and the Royal Zoological Society of Scotland.

Natural England - formerly English Nature - is thinking of conducting a similar experiment south of the border.

Sir Martin Doughty, the organisation's chairman, said: "Beavers hold water back in rivers and help prevent flooding, so we might look at a reintroduction - possibly in the New Forest."

Best known for their natural trait of building dams in rivers, the semi-aquatic creatures used to be an important part of England's fauna.

But they were hunted for their pelts, meat and castoreum - an oil secreted by glands beneath their tail and thought to have medicinal properties.

By the end of the 19th century they were reduced to a few isolated sites near rivers in France, Germany and Norway.

Since the 1920s beavers have been reintroduced in 13 European countries and by the early 1990s the number of beavers in Europe was thought to total about 250,000.

Moves to reintroduce them in Britain are likely to prove popular with wildlife enthusiasts and ecology experts.

Beavers have a unique ability to improve the habitat in which they live. Their dams, built to enable them to swim to potential food sources, create ponds that support a wide range of species.

The dams also regulate flooding and improve water quality by trapping large amounts of silt that would otherwise flow down the river.

Martin Noble, formerly the Forestry Commission's chief keeper in the New Forest, said: "As a wildlife habitat the area would benefit greatly from the reintroduction of beavers.

"They do wonderful work in creating ponds and wetland habitats.

"That could result in the loss of grazing land in the Forest, but it's a natural environment that should be managed by natural forces."