Outbreak of crayfish plague in River Barrow confirmed

Large number of dead engangered species reported as biosecurity measures introduced

White clawed crayfish (Austropotamobius pallipes) underwater on riverbed, River Leith, Cumbria, England, UK. File photograph

Large numbers of dead freshwater crayfish have been reported in the River Barrow from Carlow to Graiguenamanagh, Co Kilkenny, in recent days.

The outbreak of crayfish plague has been confirmed using DNA analysis.

This is the fifth Irish outbreak of the disease in the past two years. If it spreads further, there are concerns the disease 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) – part of the Department of Culture, Heritage and the Gaeltacht – Inland Fisheries Ireland and the Marine Institute.


The kill only affects white-clawed crayfish; other freshwater animals and people are not affected. The disease usually causes 100 per cent 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,” according to the NPWS.

It added: “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.”

The crayfish plague organism, a parasitic fungus, 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. Previous outbreaks occurred on the Erne/Bruskey waterway in Co Cavan; River Suir in Co Tipperary, River Deel Co Limerick and Lorrha River in north Tipperary.

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

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 (eg 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.

The smaller native species has been decimated in Europe by the impact of the plague which spread 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.

There is no evidence to date that non-native freshwater crayfish have been introduced to Ireland, but there are indications that American crayfish for sale here online

Many American crayfish species are resistant to crayfish plague but can act as disease carriers. It is illegal to deliberately release any non-native species of crayfish into Irish freshwaters.

If the crayfish plague becomes established there is a high probability the white-clawed crayfish, which is protected under Irish Law and the EU Habitats Directive, will be eliminated from much of the island. “Furthermore, this could have a severe impact on habitats – destabilising canal and river banks by burrowing – and other freshwater species, such as salmon and trout fisheries,” the NPWS said.

Kevin O'Sullivan

Kevin O'Sullivan

Kevin O'Sullivan is Environment and Science Editor and former editor of The Irish Times