An outbreak of crayfish plague on the River Blackwater could wipe out the total population of white-clawed crayfish - a protected species under Irish Law and the EU Habitats Directive - in the catchment area.
The shellfish is a globally threatened species and Ireland holds one of the largest surviving populations.
First discovered in Ireland in 2015 in Co Cavan, crayfish plague has spread to several other rivers across the country.
However, this is the first recorded outbreak of the deadly crayfish plague in Co. Cork.
While harmless to people, pets, livestock and all other freshwater organisms, the National Parks and Wildlife Service and Inland Fisheries Inland say the impact of the plague is devastating, causing 100% mortality of white-clawed crayfish.
Given experiences elsewhere, a total kill of the crayfish population is expected, which both say will have "major consequences for the ecology of the Blackwater, Awbeg and the whole of the Munster Blackwater catchment".
The River Blackwater is very popular with anglers, kayakers and other recreational users who are being urged to operate a 'Check, Clean and Dry' protocol for fishing and water sports equipment.
This involves routine checking, cleaning and drying of equipment after leaving a river and before entering another water body.
The agencies warn that if the crayfish plague continues to spread, there is a high probability that the white-clawed Crayfish will become extinct from most rivers in Ireland.
It is believed the spread of the plague is solely due to human activities and lack of biosecurity.
