River Eden
Safety notes for members and visitors
Crayfish Plague
The Eden Rivers Trust


Environment Agency sources have revealed that around 30 mature adults of the American Signal Crayfish were found in the River Glenderamackin at Threlkeld, a stone’s throw from PAA waters

Crayfish Plague

Crayfish plague (caused by the fungus Aphanomyces astaci) has caused drastic losses of native crayfish in rivers in England.  It is believed that this disease was introduced and is spread by the most frequently farmed species, the North American signal crayfish (Pasifastacus leniusculus) a carrier of the disease.

Cumbrian rivers and becks support some of the last remaining populations of the native white clawed crayfish - the Eden system is still free of this virulent disease and Penrith Anglers would urge any member, who fishes on other waters or any visiting angler, to be vigilant and follow the precautions listed below.

The difference between native white clawed crayfish and the signal crayfish







Signal Crayfish up to 30cm long
Underside of claws = red

Native white-clawed crayfish up to 12 - 30cm long
Underside of claws=dirtywhite/pink
Claws = red

How Crayfish Plague is spread 
Disease precautions are essential to prevent the spread of crayfish plague (Aphanomyces astci), which produces free-swimming zoospores that are specific to crayfish and can be carried in water and mud and on damp equipment. The risk of picking up spores is greatest at times of a plague outbreak, when the number of zoospores is high.

The fungal spores of crayfish plague spores can survive for up to two weeks in water, but can be killed by drying or disinfecting. .

Introducing signal crayfish into water previously free of the disease can spread crayfish plague.

It can also spread on people’s wet footwear and equipment.

Preventing the spread of crayfish plague

  • As the spores remain viable only when damp, complete drying of equipment that has been in contact with water or sediments is an effective way of killing them. It is best to avoid fishing different rivers on the same day, alternatively dry or disinfect any boots or nets before moving between rivers. 
  • Spores can also be killed by Iodine-based (iodophors) disinfectants.

Disinfection of Equipment and Tackle

Typical iodophor products are Wescodyne/Iosan CCT and FAM 30/Iofarm, generally available from farm or dairy suppliers.

Label information and manufacturers instructions should always be adhered to, but as a broad guide, Wescodyne/Iosan CCT should be diluted 1.5 parts in 100 with water, and FAM 30/Iofarm 1 part in 100 with water.

Disinfection is best achieved by first clearing off all mud etc. followed by immersion/exposure for 5 minutes, or by application to surfaces using a spray, or pad soaked in disinfectant.

Disinfectants can be applied using a spray applicator, although it may be necessary to use a bowl to dip paddles and other equipment.    

Iodophors are inactivated by prolonged exposure to light.  When active they are a dark brown solution, becoming colourless when inactivated.  Inactivated disinfectant should not be used.     

 Always read product labels and follow the manufacturers instructions.
Chemical containers must be clearly labelled and stored in a safe and secure place; keep preparations well away from children.
Protective clothing should be worn to prevent exposure to eyes and skin when carrying out dilutions of iodophors.