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Update on Crayfish Plague in Ireland

6 Jul 2023

The Fish Health Unit at the Marine Institute has confirmed the presence of crayfish plague in the catchments below.

DNA data analysis from both crayfish mortality samples and also water filtration samples (environmental DNA) was used to generate this map. Please see section below on the National Crayfish Plague Surveillance Programme for further details.

DNA analysis by the Fish Health Unit at the Marine Institute has confirmed the presence of crayfish plague in the above locations

What is Crayfish Plague?

It is a highly infectious lethal disease caused by a fungal-like organism, Aphanomyces astaci, which infects white-clawed crayfish and can cause up to 100% mortality. 

It is recognised as a very significant threat to the survival of the globally threatened White-Clawed Crayfish (Austropotamobius pallipes), the only crayfish species native to Ireland.

Genotyping analysis by WOAH reference laboratories in the UK and in Finland have shown there are at least 3 different genotypes of Aphanomyces astaci present in Ireland thus far. This genetic diversity suggests there have been at least 3 separate introductions of the disease into the country. This has highlighted an urgent need for a better understanding of the possible sources of the disease, its routes of transmission, and its current spread.

The first confirmed outbreak of crayfish plague in Ireland occurred in 2015 in the Bruskey River, a tributary of the Erne, and since then it has been detected in a growing number of rivers/catchments on the island which include: Suir, Deel, Barrow & Lorrha (2017); Ulster Blackwater, Clare & Al (2018); Nore, Maigue, Slate & Shannon (2019); Clodiagh [Shannon 25A], Moy and Sligo (2021); Munster Blackwater (2023). Further analyses are ongoing to establish if there may be any link between these and previous outbreaks of Crayfish plague.


Biosecurity Measures: For All Waterways Users

The spores of A. astaci can survive for several weeks and can be transported between river & lake systems on damp clothing, equipment, boats, or machinery. Any site within an affected catchment should be considered high risk.

Anyone involved in activities in any watercourse 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 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 as the infectious spores are destroyed by desiccation. Care should be taken with boats to ensure water is removed from the inside. The crayfish plague organism can be carried on wet equipment to new sites and spread to other unaffected populations in Ireland.

The 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.

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 the Biodiversity Data Capture app.


National Crayfish Plague Surveillance Programme

In an effort to assess the prevalence of Aphanomyces astaci nationally and investigate the potential presence of non-native crayfish species which may have introduced the pathogen into Ireland; the National Crayfish Plague Surveillance Programme, jointly funded by National Parks & Wildlife Service (NPWS) & Marine Institute, was established in 2018.

This surveillance programme uses the latest environmental (e)DNA methodologies to detect the presence of Aphanomyces astaci in water from selected sample points in all catchments/sub-catchments where white-clawed crayfish are known to be present (34 areas in total).

The first phase of sampling for the surveillance programme ran from August 2018 until December 2018 to coincide with the crayfish moulting/reproduction season. Sample collection involves collecting water samples from 6 sampling sites on each of the 34 catchments. Water samples are then filtered on site and these filters are frozen for subsequent analysis using eDNA technology.

Reports on the surveillance programme can be downloaded at the following links:

Further details on the Surveillance Programme can also be requested from