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Crayfish Plague warning for rivers Shannon and Al region       printable version
10 Nov 2018 filed by editor - General, Environment

All water users along the River Shannon are being urged to take precautions after confirmation of an outbreak of Crayfish Plague (which kills native freshwater White-clawed Crayfish) on a stretch of the Al River. This River is one of the main tributaries to the River Shannon in Athlone and flows westerly to its confluence entering the Shannon downstream of the weir.

A small number of dead freshwater crayfish were reported on the river last week. DNA analysis by the Marine Institute has now confirmed that crayfish were infected with the fungus-like organism responsible for causing Crayfish plague. Further analyses are still ongoing to establish if there may be any links between this and previous outbreaks of Crayfish plague.

Crayfish Plague only impacts native White-clawed Crayfish. Fish and other freshwater animals are not affected. The disease only infects species of crayfish and experience elsewhere indicates the disease can cause up to 100% mortality in white-clawed crayfish species. Agencies including the National Parks and Wildlife Service, Westmeath Municipal and County Councils will be working together to erect signage along the Al River and information will be on the Westmeath County Council web site.

Crayfish Plague is recognised as a very significant threat to the survival of the globally threatened White-Clawed Crayfish in Ireland.

The disease is considered fatal to all infected native crayfish and the experience in other countries is that where outbreaks occur there is complete extermination of White-clawed Crayfish populations.

The disease is spread invisibly in water and the infectious stage may be moved to other river and lake systems on equipment, boats and machinery.

<< Protected White-clawed crayfish (D. Gerke)

The disease comes from North American species of crayfish which are now widespread in the UK and on the continent of Europe. To date there are no known records of these American species in Ireland and it is against the law to bring them into Ireland, to sell them, distribute them or release them.

This is the seventh confirmed outbreak of the disease in the whole of Ireland since it was first found in 2015 in County Cavan, followed by 4 separate confirmed outbreaks in 2017 and 1 confirmed outbreak in Northern Ireland earlier this year. The closest known previous outbreak to this was one in the Lorrha in Co. Tipperary. How the disease could have come to the River Al is not known.

Biosecurity Measures
Anyone involved in activities in the Al River and River Shannon should observe the 'Check, Clean and Dry' protocol once they leave the river and before visiting any waterway again. This includes community and local authority clean-up groups, survey work as well as anglers and all recreational water uses. All wet gear (boats, clothing and equipment) should be checked for any silt or mud, plant material or animals before being thoroughly cleaned and finally dried. Disinfectant or hot water (over 40 degrees Celsius) should be used to clean all equipment and this should be followed by a minimum 48 hour drying period (preferably longer up to a week).

The drying period is especially important in ensuring that all equipment is clear of infectious organism, including the removal of any water inside the boat. The crayfish plague organism can be carried on wet equipment to new sites and containment of the outbreak is essential to prevent spread to other unaffected populations in Ireland.

The apparent spread of Crayfish Plague in Ireland over the last few years highlights the need to observe the 'Check, Clean and Dry' protocol as matter of routine for all users of waterways in Ireland.

Importance of White-clawed Crayfish
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.

If Crayfish Plague becomes established there is a high probability that the White-clawed Crayfish, which is currently protected under Irish Law and the EU Habitats Directive, will be eliminated from much of Ireland. If non-native crayfish are found to be established in Ireland, this could have a severe impact on habitats as they can destabilise canal and river banks by burrowing. It could also impact other freshwater species, such as salmon and trout fisheries.

SI 354/2018, the European Union (Invasive Alien Species) (Freshwater Crayfish) Regulations 2018, bans the import, sale, keeping or release the introduction of several species of non-native crayfish which have been included on the EU list of invasive alien species of Union concern ('the Union list').  This includes the signal crayfish, the marbled crayfish and the red swamp crayfish.At this time however, there is no evidence that non-native freshwater crayfish have been introduced in this country.

The public are asked to follow the 'Check, Clean and Dry' protocol when using the waterways and to alert the authorities of any mass mortality of crayfish as well as sightings of unusual crayfish (e.g. red claws, large size).

National Parks and Wildlife Service ( )

National Biodiversity Data Centre ( )

Inland Fisheries Ireland ( )

Anyone who sees any dead or dying crayfish should report this to National Parks and Wildlife Service, Westmeath County Council or Colette O'Flynn at the National Biodiversity Data Centre, Waterford (email:

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 or direct to Colette O'Flynn (email: Phone: 051 306248

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.

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: 

Information on the Check, Clean, Dry protocol is available from the GB Non-native Species Secretariat web site

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