The Shannon Regional Fisheries Board believes it has identified a source of agricultural pollution which caused a major fish kill in the Ballinahowna river, outside Ballinagare, Co Roscommon, at the end of last month.
The pollution, which caused the deaths of some 2,000 fish, could set the popular trout nursery back a decade, according to local anglers.
A fisheries board spokesman confirmed yesterday it was investigating legal action against the individual who it believed was responsible for the kill.
Fines of up to £2,000 can be enforced in the District Court for a conviction for a pollution which leads to a fish kill. Should the board decide to prosecute the case in the Circuit Court, the fines could be as high as £5,000.
The board said the river appears to be "completely wiped out". Some £20,000 has been spent on salmonoid rehabilitation works by the board in recent years in the river.
Meanwhile at Lough Derg, signs on the Tipperary lakeshore, which advise against bathing due to pollution from algae, remain in place despite the water recently testing clear of pollution. A spokesman for Tipperary North Riding County Council said the signs would remain in place as a precaution.
Water samples taken from the Co Galway and Co Clare sides of the lake continue to suggest the water there is safe for bathing.
In another angling-related development, members of the Connacht branch of the Trout Anglers' Federation of Ireland will meet in the Longford Arms hotel, Longford Town, tonight to discuss fears that a new power station at Termonbarry could affect fish stocks.