Since the alert was raised on Monday, up to 650 dead adult salmon and trout have been taken from the polluted waterway near Kilmallock.

Michael Fitzsimons, senior fisheries environmental officer with Inland Fisheries Ireland who is overseeing the situation, said the total scale of the fish kill has not been ascertained, as the fish taken from the river were found in just about half the 8km stretch of the Lubagh.

Mr Fitzsimons said that, based on the number of trout and salmon who died, he estimates up to 400 smaller, juvenile fish were also lost.

He said the amount of slurry involved was “substantial”. Local sources told the Irish Examiner that as much as 50,000 gallons got into the waterway from a farm slurry tank.

“We will have to wait and see the full extend of the damage and there is an ongoing evaluation and analysis of samples taken from the river,” Mr Fitzsimons said.

He said he was in constant contact with environmental officials from Limerick City and County Council. Both Inland Fisheries Ireland and the council have powers to take prosecutions in cases involving river pollution.

Mr Fitzsimons said it was too early to speculate on a possible prosecution as the investigation is ongoing.

Eamonn O’Riordan, chairman of Kilfinan and Kilmallock Anglers Association, said it will take three to four years to renew fish life in the river.

“We can’t turn back the clock and we can’t put the fish back into the river. We will just have to move forward. The amount of young fish lost will never be calculated as they were the first casualties and have been taken down the river. To see so many fish dead is awful.”