INLAND FISHERIES IRELAND has said that the major fish kill in Co Cork last month may have been caused by chronic exposure to a chemical agent.

Up to 46,000 fish died on a 30km section of the River Blackwater between Lombardstown and Killavullen in North Cork.

The fish kill was first discovered by anglers on the morning of Monday, 11 August. The Journal has confirmed that no sampling took place by IFI until a full 24 hours later.

The Environmental Protection Agency (EPA) found no causal link between discharges from nearby businesses and the major fish kill.

In a statement this afternoon, IFI said it is continuing to investigate the incident and is deploying “a range of operational activities” to try to find a cause.

The Marine Institute carried out diagnostic testing of fish samples on 14 August, which found that there was no evidence of bacterial infection, systemic disease, specific viral infections, or a specific parasite noted in test samples.

“However, gill pathology was consistent across the samples and suggested possible chronic exposure to a chemical agent,” the IFI said. 

“This indicated that an event had happened in the days before the first report was made to IFI.”

The state agency said it has sent 28 brown trout specimens from an affected stretch of the river for extensive laboratory testing to identify any contaminants in their bodies.

The testing is checking for the presence of a variety of potentially harmful substances in their systems, including heavy metals, chemicals, and pesticides, and the IFI said the result could direct the next steps in its investigation.

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The agency said it is also carrying out further habitat inspections on the River Blackwater to assess the scale of mortalities and waters affected. More than 110 habitat inspections at 45 locations have been completed since the report of the fish kill on 11 August. 

It is also deploying drone and kayak patrols over an extended area of river channel to continue to examine and survey the scene, as well as quantifying the number of fish that may have died in the incident using historic population records. 

Mortalities observed by IFI were included in a mixture of healthy and sick fish throughout the affected channel, and were predominantly brown trout.

Residue test results are due to be sent to IFI tomorrow. These will be published following an examination of the data by members of the inter-agency group, including Cork County Council, the EPA, the Marine Institute and Uisce Éireann. 

The IFI said clubs and fishery owners will be contacted individually regarding assessments of the effects of the fish kill.