The Department of Climate, Energy and the Environment has said that no specific factors have been identified which might have caused a large scale fish kill in the River Blackwater in Co. Cork.

This follows extensive laboratory testing of 28 brown trout specimens as part of the investigation into the incident.

Those laboratory results, along with other investigations, have not turned up any specific cause of the incident.

Technical teams involved in the investigations have concluded that the most likely cause of the fish mortality was an irritant in the water, but the source and specific compound cannot be determined based on investigations.

The laboratory results included a residual heavy metals report and extensive residue testing data, checking for the presence of hundreds of potentially harmful substances.

According to the department, investigating agencies have used all available resources to monitor the catchment.

This includes extensive surveys, site visits and testing by the various agencies contributing to the investigation, including the Environmental Protection Agency (EPA), Cork County Council, Inland Fisheries Ireland (IFI), the Marine Institute; and Uisce Éireann.

Angling is continuing on the Blackwater, with no water quality issues currently detected.

Uisce Éireann monitoring results from the Mallow water treatment plant to date have shown that the water is safe to drink.

All agencies are continuing to carry out ongoing and routine surveys and inspections to identify potential risks, both in the Blackwater catchment and more widely across other water courses, the department said.

The inter-agency group which oversaw the investigations will now conduct a review of actions taken by all agencies involved, including full and comprehensive findings from all investigations and recommendations for future action.

Commenting on these findings, Minister of State for fisheries and the marine Timmy Dooley said: "It is deeply regrettable that the extensive work carried out to get to the bottom of this incident has not yielded any definitive results.

"I have requested a comprehensive inter-agency report on the investigation into this incident, as it will be important to understand how we can streamline our cross-agency response to these incidents, and ensure that we are identifying the sources of toxic pollutants in our catchments as quickly as possible," Minister Dooley added.

"It is essential that our agencies work with all stakeholders to ensure that our prevention, compliance and incident response actions are as effective as possible," the minister said.