The third major fish kill this summer, which has led to at least eight miles of the Mulkear river in Co Limerick being "wiped out", was caused by agricultural effluent. Fertiliser pollution has also led to the closure of the Lakes of Killarney to fishing and swimming, with the cancellation of three main angling events.
Details of the Limerick fish kill emerged as the Munster Regional Angling Council announced the cancellation of a number of prestigious angling events on the lakes.
The Minister for Marine and Natural Resources, Dr Woods, said those found responsible for fish kills would "face the full rigours of the law".
Laws introduced in 1990 mean guilty parties can face fines of up to £25,000, five years in prison or both. They can also be made pay towards the recovery of the river, which in the Mulkear case could cost up to £10,000.
Dr Woods said he was seeking a meeting with agricultural representative bodies to express his deep concern about fish kills.
The first reports of the Mulkear kill were made on Wednesday about midnight. At first light yesterday, officials of the Shannon Regional Fisheries Board, Limerick County Council and the ESB were at the river and discovered the extent of the disaster.
The cause was identified as being at the upper part of a tributary of the Mulkear, the Dead river, at Pallasgrean near the Tipperary-Limerick border. Effluent was still flowing from a ditch close to the river last night and officials were working to stem the flow.
The river stank of the effluent. All day officials worked to take live and dead fish from the water. A "conservative estimate" of 20,000 to 30,000 dead fish has been arrived at, but chief officer of the regional fisheries board, Mr Eamon Cusack, said the figure could be as high as 80,000 to 100,000. He said it could take two to three years for the river to recover. It is popular with Irish and foreign anglers and is the basis of local tourism.
The kill follows similar incidents last month in Co Meath and Co Cork. The Moynalty river in Co Meath, was destroyed in a fish kill which followed a fire upstream in a chemical factory in Mullagh, Co Cavan, on July 28th. At least 100,000 fish were killed.
On July 18th, pig slurry from a Macroom Farm Mills plant at Grenagh in north Cork caused a similarly large fish kill in the Martin and Shournagh rivers.
However, Mr Cusack said that "point source" incidents such as these are occurring less frequently. "The big worry now is the eutrophication of rivers and lakes," he said. Phosphates from fertilisers are being washed into rivers and lakes and causing eutrophication or algal blooms. The blooms use up oxygen supplies in the water and kill off fish.