Final report: No definitive cause of Blackwater pollution that killed 32,000 fish

Despite extensive investigations, no evidence was found of a link between the fish kill and an identifiable pollution incident, or a specific environmental exposure, or waterborne irritant.

A 102-page report into a pollution incident that killed 32,000 salmon and brown trout in the River Blackwater in Cork has found no identifiable cause of the fish kill. 

An inter-agency group, including the Environmental Protection Agency, Inland Fisheries Ireland, Cork County Council and other agencies, has released a final report on what is believed to be Ireland's largest recorded single fish kill. 

Despite extensive investigations, the group could find no evidence of a link between the fish kill and an identifiable pollution incident, or a specific environmental exposure, or waterborne irritant.

There was also no evidence of a chronic problem with water quality before or after the fish kill, or any evidence of a systemic disease in the dead fish.

The inter-agency group suspect a waterborne agent had a likely entered the River Blackwater around August 5 or 6, and that the first dead fish were found 72 hours later.

The report said the pollutant dissipated quickly, rendering it undetectable in water samples and fish tissue samples.

There was no evidence that protected species, such as otter or freshwater pearl mussels, were impacted. 

The expert group said it is likely that a short-term pollution event caused the fish kill, but this has not been traced to any industrial, commercial, or agricultural operation. 

As part of the probe, the EPA investigated industrial facilities, wastewater treatment plants and drinking water plants but it could establish no causal link between these activities and the fish kill. 

Separate investigations of light industrial sites and agricultural operations also found no causal link.

The fish kill had had a serious impact on local fish stocks, with some estimates that it could take 10 years to recover.