Further testing of fish that were killed in the River Blackwater last month has found that no specific factors could be conclusively established as to the cause of the fish kill.
Minister of State with responsibility for fisheries and the marine Timmy Dooley this week chaired the fifth inter-agency group investigating the recent fish mortality incident on the River Blackwater.
“Following extensive laboratory testing of 28 brown trout specimens as part of the investigation, the group was briefed by a technical subgroup on their interpretation and analysis.
“These results, alongside inter-agency investigations to date, have found that no specific factors could be conclusively established as to the cause of death of the significant number of fish affected in this incident.
“Technical teams 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 Environmental Protection Agency (EPA) has said.
Surveys and site visits
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:
41 inspections by the EPA to 31 regulated sites.40 samples, associated with EPA regulated facilities, taken and analysed.Five macroinvertebrate quality surveys carried out by the EPA in the Kanturk to Mallow area on 12 August, and 1 and 2 September 2025.Assessment of monitoring data from EPA-regulated facilities as far back as 28 July.20 inspections of local government Section 4 licenced discharges and a number of commercial activities conducted by Cork County Council.14 inspections of agricultural activities to examine herbicide or pesticide use and GAP compliance by Cork County Council.Nine SSRS macroinvertebrate assessments carried out by the council, as well as sample testing and analysis.Residue sampling commissioned by Inland Fisheries Ireland (IFI), with over 900 compounds tested for – including heavy metals, pesticides and chemicals.200 habitat inspections and 10 macroinvertebrate surveys completed by IFI, including an electrofishing boat survey.Diagnostic testing carried out by the Marine Institute to evaluate disease presence and overall condition of the fish.Uisce Éireann has reviewed drinking water results to ensure water is safe to drink. Drinking water
Angling is continuing on the Blackwater, with no water quality issues currently detected. Uisce Éireann undertakes monitoring of drinking water supplies in accordance with the requirements of the drinking water regulations.
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 group 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, both in relation to the River Blackwater catchment and other river ecosystems.
Minister Dooley said that it is deeply regrettable that the extensive work carried out to get to the bottom of this incident has not yielded any definitive results.
Read more
Further lab results expected from Blackwater fish kill this week
No link between North Cork and fish kill, says EPA
'We are operating normally' - North Cork Creameries
'No evidence' bacteria responsible for Blackwater fish kill - IFI
Further testing of fish that were killed in the River Blackwater last month has found that no specific factors could be conclusively established as to the cause of the fish kill.
Minister of State with responsibility for fisheries and the marine Timmy Dooley this week chaired the fifth inter-agency group investigating the recent fish mortality incident on the River Blackwater.
“Following extensive laboratory testing of 28 brown trout specimens as part of the investigation, the group was briefed by a technical subgroup on their interpretation and analysis.
“These results, alongside inter-agency investigations to date, have found that no specific factors could be conclusively established as to the cause of death of the significant number of fish affected in this incident.
“Technical teams 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 Environmental Protection Agency (EPA) has said.
Surveys and site visits
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:
41 inspections by the EPA to 31 regulated sites.40 samples, associated with EPA regulated facilities, taken and analysed.Five macroinvertebrate quality surveys carried out by the EPA in the Kanturk to Mallow area on 12 August, and 1 and 2 September 2025.Assessment of monitoring data from EPA-regulated facilities as far back as 28 July.20 inspections of local government Section 4 licenced discharges and a number of commercial activities conducted by Cork County Council.14 inspections of agricultural activities to examine herbicide or pesticide use and GAP compliance by Cork County Council.Nine SSRS macroinvertebrate assessments carried out by the council, as well as sample testing and analysis.Residue sampling commissioned by Inland Fisheries Ireland (IFI), with over 900 compounds tested for – including heavy metals, pesticides and chemicals.200 habitat inspections and 10 macroinvertebrate surveys completed by IFI, including an electrofishing boat survey.Diagnostic testing carried out by the Marine Institute to evaluate disease presence and overall condition of the fish.Uisce Éireann has reviewed drinking water results to ensure water is safe to drink. Drinking water
Angling is continuing on the Blackwater, with no water quality issues currently detected. Uisce Éireann undertakes monitoring of drinking water supplies in accordance with the requirements of the drinking water regulations.
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 group 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, both in relation to the River Blackwater catchment and other river ecosystems.
Minister Dooley said that it is deeply regrettable that the extensive work carried out to get to the bottom of this incident has not yielded any definitive results.
Read more
Further lab results expected from Blackwater fish kill this week
No link between North Cork and fish kill, says EPA
'We are operating normally' - North Cork Creameries
'No evidence' bacteria responsible for Blackwater fish kill - IFI
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