Otters, once familiar residents of many British rivers, are beginning to reappear in some of their old haunts, say conservationists.

The government has set a target of restoring otters to all UK rivers by 2010. And the Wildlife Trusts say that goal "looks ever more achievable".

The Trusts, the national liaison body for the 46 county wildlife trusts, last year launched an Otters and Rivers Project with 20 full-time staff and more than 500 volunteers.

It is part of the government's UK Biodiversity Action Plan, a series of rescue programmes for endangered species and habitats.

Water UK, the water industry's representative body, is supporting the project with �1.5m in sponsorship.

Progress over past year

Saved from extinction

During the past year, the Trusts say in a progress report, areas to which otters have returned include several rivers in Norfolk and four tributaries of the upper Trent.

Water quality improvements have also enticed them back to a river they had abandoned in Warwickshire.

And for the first time in 20 years there has been a sighting - so far unconfirmed - of an otter in Poole Harbour in Dorset.

Elsewhere in the county there have been the first signs of otters in a quarter of a century. There has even been news of the animals at a sewage works on the outskirts of Derby.

The Director General of the Wildlife Trusts, Dr Simon Lyster, says: "Otters are fantastic indicators of the health of our rivers and waterways".

"So their success spells good news for other species too. Any work for otters not only helps safeguard their habitats, such as chalk rivers, ancient water meadows, reedbeds and fens, but it also benefits other endangered species.

"For example, a river harbouring otters may also be a haven for the water vole, the native white-clawed crayfish, and the freshwater pearl mussel."

Saved from virtual extinction

As recently as the 1950s, otters were common and widespread. But from then on they declined sharply, mainly because of pollution from farm pesticides, and habitat loss.

Twenty years ago the species was almost extinct in most of England, parts of Wales and some areas of Scotland.

But the otter's gradual return began with the phasing out of chlorinated hydrocarbon pesticides, which with other chemicals built up in fish including eels, the otter's prey of choice.

The Trusts say the animal's distribution "is now wide but sporadic throughout the British Isles and Ireland".

"The strongest populations remain in Wales, southwest England and much of Scotland, where sea loch and coastal colonies are among the largest in Europe.

"There is also a significant population in northern Ireland."