Investigation concludes into Blackwater fish deaths but cause remains unknown
Up to 32,000 fish died in Blackwater river but cause unknown despite major investigation.
An exhaustive inter-agency investigation into the deaths of up to 32,000 salmon and brown trout in the Munster Blackwater has concluded without identifying a definitive cause, despite extensive testing by multiple state agencies.
Minister of State for Fisheries and the Marine Timmy Dooley welcomed the publication of the summary report today, following the establishment of an inter-agency group on 22nd August to investigate the serious fish mortality incident that shocked local communities.
The investigation, led by Inland Fisheries Ireland (IFI) and supported by the Environmental Protection Agency, Cork County Council, and six other state agencies, conducted extensive sampling, testing and monitoring across the river catchment.
Minister Dooley said:
"The extensive fish mortalities that occurred on the River Blackwater represent a serious impact to local fish stocks and have had a deeply negative impact on surrounding communities."
He added:
"In this instance, a definitive cause could not be identified despite the extensive and significant investigation by members of the inter-agency group."
The report concludes that a waterborne irritant likely entered the river up to 72 hours before the first dead fish were observed, most probably upstream of where mortalities were initially discovered by IFI. The substance dissipated quickly, making it undetectable in subsequent water and tissue samples.
Minister Dooley emphasised:
"The findings in the report do give reassurance that this was a short-lived event, with no evidence of ongoing pollution risks."
Angling continues on the Blackwater with no current water quality issues detected. Uisce Éireann's monitoring of drinking water supplies shows that water from the Mallow treatment plant remains safe to drink, meeting all regulatory requirements.
The investigation involved IFI, the EPA, Cork County Council, Marine Institute, Uisce Éireann, Department of Agriculture, Health Service Executive, National Parks and Wildlife Service, and the Local Authority Waters Programme.
While fish populations are expected to recover naturally, agencies acknowledge the significant impact on the area's angling community and local ecosystems. The learnings from this incident will inform future inter-agency responses to similar environmental emergencies across Ireland.
The full summary report is available on Inland Fisheries Ireland's website.
