A “rescue mission” for native crayfish is under way in Northumberland after a population were found dead with mysterious patches on their shells.

The Environment Agency is working to save the internationally important species of native white-clawed crayfish in the River Wansbeck by searching for females with eggs to be taken and reared in a hatchery.

At least 100 individuals of the endangered species, which is the UK’s only native freshwater crayfish, have been found dead since the end of September and environment experts are perplexed as to what is causing the “concerning” mass die-off.