The zebra mussel, a dreaded marine pest, has been discovered for the first time on 14,000-acre Lough Conn, Co Mayo, which is a prime salmon and trout fishery.
Two young zebra mussels were found during a summer monitoring programme on the lake carried out by the North Western Regional Fisheries Board in conjunction with Sligo Institute of Technology. Local anglers and fishermen reacted with shock and dismay.
Zebra mussels multiply rapidly into dense clusters. Fishery interests and ecologists are seriously concerned by the discovery as infestation irrevocably affects the ecology of a water body, with major long-term implications for fish stocks.
They were first recorded in Ireland in 1993, when it is believed they arrived on boats from England or The Netherlands. They quickly spread throughout the Shannon system and were discovered in recent years in Lough Gill and Lough Arrow in Co Sligo.
Sightings of adult zebra mussels are expected on Lough Conn next year, with a high population increase in subsequent years.
The Lough Conn discovery has heightened concern about the possible spread of the species to the Loughs Carra, Mask and Corrib system, where a highly invasive weed, lagarosiphon major, is already posing a threat to fisheries on Lough Corrib.
Vincent Roche, chief executive of the North Western Regional Fisheries Board, said the discovery in Lough Conn highlighted the need for increased efforts by all lake users to prevent the spread of zebra mussels.
He urged anglers, eel fishermen, jet-ski owners and other lake users to comply with the guidelines which have been put in place by the Western Region Zebra Mussel Control Initiative to prevent the spread of the species. He said the board would be reviewing its own operations and putting measures in place to ensure zebra mussels could not be spread to other water bodies in the region by the board's boats and equipment.
Dr Francis Lucy, an expert in zebra mussels at Sligo IT, said it was likely that the mussels were introduced to the lake by a boat.
Zebra mussels are thumbnail-sized shellfish that consume the plankton which small fish depend on. As well as ecological damage, they create problems for boat owners and can clog water pipes.