The white-clawed crayfish is Britain's only native crayfish.

The signal crayfish, which carries a plague that can wipe out the native white-clawed crayfish, has been spotted in a catchment of the River Derwent.

The Environment Agency said the find was a "devastating blow".

It fears the species could spread to the adjacent Eden catchment which is home to the best native population.

Signal crayfish have devastated native populations across England through direct competition and the transfer of crayfish plague, which is transferred by spores.

Salmon threat

Spores can travel on anything wet, including fishing gear, mud on vehicles or other equipment, as well as being transferred via birds and animals.

A member of the public contacted the Environment Agency after spotting the signal crayfish at St Johns Beck near Threlkeld.

The agency's Gail Butterill said: "Not only does it pose a threat to salmon spawning but it has broader negative impacts on plant and invertebrate communities and river bank stability.

"We are urging anyone who thinks they have seen a crayfish in any tributaries of the River Derwent to contact us immediately."

The agency is investigating the extent of the infestation and the source and discussing with English Nature possibilities for control or eradication.

Ms Butterill urged anyone in contact with water in the Greta Catchment to wash thoroughly and dry or disinfect all equipment before using in any of the Eden, Kent or Leven catchments.