NATURE conservationists have been dealt a devastating blow as an alien species has been discovered in a tributary of the River Wear.

An American signal crayfish was found in the River Gaunless, which The Wear Rivers Trust (WRT) describes as "very bad news" for the river ecosystem.

The highly invasive aliens are effectively eating machines, feeding on native invertebrates and fish eggs.

They can be so damaging that once they have finished eating every other living organism they can turn on each other, leaving behind a trail of destruction.

Steve Hudson, project officer for WRT, a charity that works to conserve, protect and rehabilitate the landscape and watercourses of the whole River Wear catchment, said: “This could be very damaging for the watercourse.

“The American signal crayfish have a ferocious appetite and also damage the river banks through burrowing.

“They could have made their way here in a multitude of ways, and it is difficult to pinpoint the source whether it be flown in on birds or ducks, carried in on vehicles, via anglers waders or canoeists paddles.”

The species first made it across from America to the UK in 1976.

They have since become widespread across the country and are not only vicious feeders but also carriers of crayfish plague which has put the native white-clawed crayfish on the endangered list.

It is unknown how they ended up in the Gaunless, which runs from Copley to Bishop Auckland, but they could have been flown in on birds or carried in on vehicles, by anglers or canoeists.

Environment manager Fiona Morris, from the Environment Agency, said: “All we can do is try our best to contain them and stop them from spreading, to help protect our native crayfish and other wildlife.

“In the North East we still have native populations which are holding out against any invasion, and we want to keep it that way.”

River users and anglers who use the River Wear and its tributaries are urged to be vigilant to help stop the spread of the American signal crayfish in the region’s waterways.

They are asked to check, clean and dry all equipment, clothing and footwear thoroughly.

Mr Hudson added: “We would like to appeal to the public to inform us of any sightings of this species of crayfish, they are instantly recognisable by the bright red colouration on the underside of the claw and also a white oval patch at the joint.”

The Wear Rivers Trust can be contacted on 01388-488867.