It could take up to 10 years for an important angling river to recover from the bogslide at Derrybrien, south Galway, the Shannon Regional Fisheries Board warned yesterday.
Fears were also growing last night about the effect of the landslide on drinking-water quality.
The board's chief executive, Mr Eamon Cusack, estimated that up to 100,000 fish could be killed as a result of the pollution of the Owendalulleegh River.
Yesterday afternoon his staff took several dead trout from the river, which feeds into Lough Cutra, which supplies water to the nearby town of Gort.
While the flooding of the Derrybrien area continued yesterday, the slide of peat and debris down the mountainside had stopped. However, locals said they feared the slide would resume as soon as it rained again.
The Owendalulleegh River holds good stocks of wild brown trout and is a spawning river for the lake. Mr Cusack said the landslide had happened at the worst possible time as the trout were beginning to move from the lake up to the river to spawn. The lake also has good stocks of pike and eel. At a fishing competition last weekend, anglers took more than 80 pike from the lake, and considered this to be an average day.
Yesterday, the river was a dark-brown colour as it flowed under a bridge close to the lake. Mr Cusack said it was difficult to see how a major environmental disaster could be avoided.
"The consequences to the fisheries environment are extremely grave," he said. "Certainly this is the worst I've ever seen."
He estimated that the river could be rejuvenated in five years if the necessary funding was made available.
A spokesman for Galway County Council said council officials were monitoring the quality of drinking-water in Lough Cutra. "There is no indication that there is a difficulty with the drinking water," he said. To minimise the risk, the council was constructing silt beds, which would draw the peat from the water before it entered the lake.
The council was also monitoring the work being done on behalf of Hibernian Wind Power, the ESB subsidiary that has been building a windfarm in the Slieve Aughty Mountains in Derrybrien.
Locals believe the landslide was caused by the construction work being done on the €60 million windfarm but Hibernian Wind Power said it was too early to establish the cause of the disaster.
Members of the Derrybrien Landslide Action Group visited the windfarm site yesterday. Mr Martin Collins, spokesman for the group, said the group had brought in their own engineering consultants to look at the issue. He did not believe a plan had been put in place by all the bodies involved. "I think there is no overall plan in place, but if there isn't, why is this work being carried out now?" he asked.
