Crayfish Plague spreads to River Barrow and water users are urged to follow biosecurity advice to contain outbreak

Large numbers of dead freshwater crayfish were reported in the River Barrow in the stretch from Carlow to Graiguemanagh. It has been confirmed using DNA analysis that the cause of death was Crayfish Plague. This is the fifth outbreak of the disease to be found in Ireland in the last two years. It is feared that if the disease spreads further, then it will threaten the survival of the entire Irish population of this endangered species.

This worrying situation is being investigated by the National Parks and Wildlife Service (NPWS) of the Department of Culture, Heritage and the Gaeltacht, Inland Fisheries Ireland (IFI) and the Marine Institute.

The kill only impacts White-clawed Crayfish; other freshwater animals and people are not affected. Experience of the disease elsewhere is that it causes 100% mortality. It is of grave concern that if the disease takes a firm hold millions of crayfish could vanish from Irish rivers and lakes in a short period of time.

All the agencies involved in managing and protecting the rivers in Ireland are concerned that another outbreak has been detected and are reiterating their advice and guidance to all users of the river to implement routine cleaning and drying of their equipment once they leave the river and before using it again. This is especially important as it is known that the crayfish plague organism can be carried on wet equipment to new sites. Containment of the outbreak is essential to prevent spread to other as yet unaffected populations in Ireland.

Waterways Ireland who manage the Barrow navigation have issued a marine notice calling all recreational, commercial, private and public body water users (boaters, walkers, swimmers, kayakers, rowers, machine operators, etc.) to operate a temporary ban on moving water sports/angling equipment and other equipment/machinery that comes in contact with the water, out of, or into the Barrow and all affected catchments.

Anyone using the river is being urged to observe the Check, Clean and Dry protocol. All wet gear should be checked for any silt or mud, plant material or animals. It then should be cleaned and finally dried. Disinfectant or hot water (over 60C) should be used to clean all equipment followed by a 24hr drying period should be adopted as standard practice in all freshwaters. Drying is especially important, including removing of any water from inside a boat and disposing of it on grass. A drying period of at least 24 hours is needed to ensure that a boat is clear of infectious organism.

People are also asked to alert the authorities of any mass mortality of crayfish or sightings of unusual crayfish that might be non-native species (e.g. crayfish with red claws, large size).

The White-clawed Crayfish is a globally threatened species and Ireland holds one of the largest surviving populations. It is the only freshwater crayfish species found in Ireland and is present in lakes, rivers and streams over much of the island. Throughout its European range, this species has been decimated by the impact of Crayfish Plague which spread to Europe with the introduction of North American species of crayfish. Until 2015, Ireland was considered free of the disease and it remains the only European country without any established non-native crayfish species.

Many American crayfish species are resistant to Crayfish Plague, but can act as carriers of the disease which is rapidly fatal when passed to the White-clawed Crayfish. The combined impact of the introduced crayfish species (which may out-compete the smaller native crayfish) and Crayfish Plague have completely eliminated the White-clawed Crayfish from much of its European range, leaving Ireland as the last stronghold of the species. The species is protected under Irish Law and the EU Habitats Directive. It is illegal to deliberately release any non-native species of crayfish into Irish freshwaters.

If Crayfish Plague becomes established there is a high probability that the White-clawed Crayfish will be eliminated from much of the island. Furthermore, if non-native crayfish are found to be established in Ireland, this could have a severe impact on habitats (e.g. destabilising canal and river banks by burrowing) and other freshwater species, such as salmon and trout fisheries. However there is no evidence to date that non-native freshwater crayfish have been introduced to Ireland.


Notes to Editors:

For further information contact Brian Nelson (01 8883294; brian.nelson@chg.gov.ie) or

Ciaran O’Keeffe (087 2646416) ciaran.okeeffe@chg.gov.ie)

Anyone who sees any dead or dying crayfish should report this in the first instance to either the Marine Institute (Deborah Cheslett Deborah.Cheslett@marine.ie) or National Parks and Wildlife Service (Brian Nelson or the local ranger).

Members of the public who suspect they have seen a non-native species of crayfish are asked to take a picture of it showing the underside of the claws and submit this through this web page http://invasivespeciesireland.com/alien-watch/ or direct to Colette Flynn (email:

coflynn@biodiversityireland.ie) Phone: 051 306248

 Further information:

White-clawed Crayfish Austropotamobius pallipes. This occurs throughout Ireland mainly but not exclusively in areas of limestone geology. It lives in a very broad range of freshwater from tiny streams and ditches to many small, medium and large lakes. The species is a generalist feeder and it in turn is a significant prey item of the Otter.

Crayfish Plague is caused by a fungus-like organism Aphanomyces astaci which is of North American origin but now occurs throughout Europe. The Crayfish Plague organism (technically an Oomycete and often called water moulds) normally grows on the outer shell of crayfish and as North American crayfish are generally immune to it, as they can prevent any infection reaching their body tissues. However, when the water mould infects White-clawed and other European crayfish, it rapidly, and fatally, spreads into the body tissues. Infected animals become distressed and behave abnormally and may survive several weeks before dying.

There have been five cases of Crayfish Plague since 2015 confirmed in Ireland affecting the Erne/Bruskey Co Cavan, River Suir Co Tipperary, River Deel Co Limerick, Lorrha River Co Tipperary and River Barrow.

Transmission of the disease has mostly been by movement of signal or other American crayfish. However spores can be carried on items that have been in contact with contaminated water, such as fishing gear, keep nets, waders and other footwear, and boats of all sorts.

Non-indigenous Crayfish. These are any species which are not native to the country. Many crayfish species have been moved within Europe and into Europe from North America and Australia. The most significant of these is the North American Signal Crayfish Pacifastacus leniusculus which is one of the main carriers of Crayfish Plague. This species is much larger than the White-clawed Crayfish and with distinctive red coloration on the underside of the claws.

Background information on the native and non-native crayfish and the crayfish plague is

available to view and print from these web pages:





Pictures of White-clawed Crayfish and Signal Crayfish are available from Colette O’Flynn at

the National Biodiversity Data Centre

Information on the Check, Clean, Dry protocol is available from the GB Non-native Species Secretariat web site http://www.nonnativespecies.org/checkcleandry/

Department of Culture, Heritage and the Gaeltacht, 23 Kildare Street, Dublin , D02 TD30. Tel: 01 631 3800 / LoCall: 1890 383 000

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