Laois County Council and the Southern Fisheries Board were last night at a loss to determine the source of pollution that killed more than 5,000 fish in a river near Durrow, the largest fish kill in the area in 16 years.
Thousands of wild brown trout, a fish highly prized by anglers, were killed in a short stretch of the River Gully, a small tributary of the River Nore. The kill is thought to be one of the largest recorded in a river of its size.
Gardaí alerted the council shortly after 9 a.m. on Thursday. Teams from the council and the fisheries board began investigating the river but have been unable to detect the source of the kill.
"We've been working consistently but we cannot tie it to a source and it's unusual that we wouldn't have an idea at this stage," Mr Sean Mullen, acting director of services with the council, said.
"Fish kills happen once or twice a year in the whole county. We've been examining agricultural holdings and side drains up and down the river, and we've had the full co-operation of the farming community. We haven't been able to establish anything yet but we'll continue searching."
The Durrow and District Anglers Club said it will take at least three years for the river to recover.
"This is a very major fish kill and it's purely affected wild brown trout. Whatever caused it didn't get into the main river, but it will be a long time before that small river will recover," Mr Michael Walsh, a spokesman for the club, said.
