A mysterious disease has wiped out thousands of roach in the twin trout and salmon lakes of Lough Conn and Lough Cullin, Co Mayo, over the past two weeks. It has led to an unpleasant smell and pollution on a number of scenic beaches in the area.
Residents and visitors have expressed concern about the number of dead fish, some of them mutilated by foraging birds, which still litter three popular bathing spots on Lough Cullin close to Foxford town.
The beaches were almost deserted over the bank holiday weekend because of fears for the water quality, despite a major clean-up instigated by the North Western Regional Fisheries Board.
Board manager Vincent Roche said yesterday that no species other than roach was affected.
The results of tests on live roach taken from the lake and sent to the laboratories of the Marine Institute were still awaited.
On Wednesday, samples from a further 10 live fish were sent to the institute for bacteriological and virus tests. Mr Roche said there was no evidence yet to back claims by a local newspaper that the cause of the fatalities was the rare tench rhabdovirus, which has never been confirmed in Ireland.
Roach were accidentally and illegally introduced to the north Mayo lakes, probably as bait by anglers, some years ago. They first appeared on Lake Derryhick, north of Castlebar, before moving into Lough Conn and Lough Cullin where they thrived on the changing water conditions, said Mr Roche.
"In the space of four years, the population of roach on the lakes has exploded."
The clean-up of dead fish along the shoreline was continuing and the board had received many calls about the smell and unsightly carcases, he said.
Concerns about the water quality on Lough Conn, which is the main source of drinking water for Ballina and a large area of north Mayo, have been allayed by Mayo County Council.