FISHERMEN, dog walkers and farmers are being urged to keep their kit clean as environmentalists fight a deadly plague which has crept into the Bybrook along the Box valley and which has killed hundreds of native crayfish over the last couple of months.

The Environment Agency recently confirmed that hundreds of the native white-clawed crayfish were infected with water fungi aphanomyces astaci, after the virus got into the stream in August, and was carried along a 8km stretch by a non-native signal crayfish.

Experts are concerned that the spores, which are invisible to the human eye, could continue to linger in the Bybrook and potentially spread to other rivers in the county.

"There is not a cure for it because it is out in the wild but we can try our best to prevent it spreading," said Harriet Alvis, of the Bristol Avon Rivers Trust.

"We are asking people to use strict biosecurity measures and check that their equipment is free, clean and dry or use an approved disinfectant to kill any spores."

In a desperate attempt to save some of the river's native crayfish, officers from the Environment Agency are moving healthy crayfish to other rivers until the plague has been eradicated.

Mike Blackmore, Wild Trout Trust's conservation officer for the south and west, who helped move crayfish after a similar outbreak in 2007, described the latest outbreak as "terrible".

"White-clawed crayfish, like wild brown trout, are a symbol of clean healthy rivers," he said.

"When you know a river should be able to support them but they simply are not there, you know something is wrong. Biosecurity makes all the difference and anyone that has been in a river needs to make sure their boots,waders, fishing tackle and dogs are clean and dry before entering a different watercourse.

"Common aquatic disinfectants like Vercon do not work on crayfish plague. The very best thing people can do is soak waders in warm water, less than 45 degrees for 15 to 20 minutes, that is the best way to kill spores."

Anyone who sees dead or dying crayfish in the area or any other environmental issue should call the Environment Agency's incident hotline on 0800 807060.