The pollution of the Mulkear River in Co Limerick, in which thousands of salmon and trout died, was caused by recent weather conditions, Limerick County Council announced last night.
A statement read: "It is the opinion of the council on the evidence available that farm effluents were not a contributory cause of this pollution."
Mr David Thompson, a prominent Co Limerick member of the Irish Farmer's Association, said last night that the council had confirmed that the pollution had absolutely nothing to do with farmers.
Exceptionally heavy rain from August 3rd to 5th resulted in the flooding of approximately 500 acres of callow land near Pallasgreen.
Extremely high water levels in the Dead River, a tributary of the Mulkear, contributed to the flooding and delayed drainage. The flooding, which lasted for up to two weeks, caused widespread decay to set in on the submerged grasslands, releasing large amounts of nutrients into the flood waters.
A council statement added: "Unseasonally high temperatures and long periods of bright sunshine contributed to the rapid rate of decay. When the high water levels in the Dead River subsided, the drainage channels which were provided as part of the original Mulkear Drainage Scheme released the highly-nutrified flood waters from the callow lands into the Mulkear River at Sunville Bridge, just north of Pallasgreen."
The breakdown of the nutrients in the flood waters resulted in severe oxygen depletion in a seven-mile stretch of the Mulkear, between Sunville Bridge and Abbington Bridge, which finally resulted in the fish kill, said the statement.
Mr David Thompson, secretary of the Mulkear Co-Op and chairman of the Co Limerick IFA animal health committee, said: "The farmers have spent billions on ensuring that the environment is protected and yet they are still blamed for anything that happens to the environment."
He called on the Environmental Protection Agency and Teagasc to investigate fully the conditions in which such an event might recur. The only way to prevent it was to introduce phase III of the Mulkear Flood Relief Programme, he added.