A large fill kill occurred in the Ollatrim River – a tributary of the Nenagh River – in Co. Tipperary last week, Inland Fisheries Ireland (IFI) has confirmed.

Fisheries officers attended the site at Ballinahemery Bridge near Ballymackey, Nenagh, Co. Tipperary, on Monday, July 9, after receiving a report.

In total, it was estimated that 14,749 fish had been killed – with dead fish observed over a 5km stretch of the river.

The species affected included brown trout (1,400), lamprey (10,500), stoneloach (805), minnow (1,820), salmon (70), crayfish (70) and stickleback (84).

IFI immediately commenced an investigation following the discovery of the fish kill.

Indications are that the incident occurred on Sunday, July 8.

This is the largest fish kill of lamprey – a protected species – in recent years and it is anticipated that recovery will take several years, IFI explained.

The investigation to identify the source of the fish kill is continuing this week.

The cause appears to have been a chemical agent, possibly a herbicide or pesticide, which has now passed through the system.

IFI is reminding the public and the farming community that if they are using spraying equipment to be aware that these herbicide and pesticide chemicals, even when diluted with water, are liable to be extremely toxic to all aquatic species and fish in particular.

Any mixing must be done far from natural watercourses – especially in the current conditions when diluting waters are in short supply, therefore increasing the toxicity of the chemical.

If mixing chemicals or washing/using spraying equipment for any purpose, particular care must be taken to ensure that the rinsing of equipment does not take place near any water body or watercourse – including small drains.

Any washing must be carried out in a manner that will not pollute the waters, the authority stresses.

IFI has a confidential hotline number to enable members of the public to report incidents on: 1890-347424.