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

Sheep dip contamination is being blamed for the latest blow to the white-clawed crayfish - the only species of crayfish native to Britain.

Ecologists said it would take years for the population at Mill Beck in Cumbria to recover.

Pollution killed almost all of the stream's crayfish in 2000.

Five years later the species was still struggling to recover, so ecologists introduced hundreds of the crustaceans into Mill Beck in 2005.

But efforts to repair the damage may have been set back several years by the latest incident.

Last stronghold

Environment Agency ecologist Brian Ingersent said: "We had a major sheep dip pollution incident in 2000 which wiped out over one thousand of the crayfish and the remaining population wouldn't have had the time to reach these kinds of numbers.

"So unfortunately the majority of the crayfish killed this month would have been those from last year's restocking."

Cumbria's waterways are some of the last remaining strongholds of native white clawed crayfish in England, a species that has been decimated in the south by pollution, the invasive American signal crayfish and disease.

Farmers are being reminded to take extra care when using and disposing of sheep dip.