‘Definite line of inquiry’ pursued over Dublin fish kill as death toll put at 1,000

The number of mortalities recorded in a fish kill on the river Tolka near Damastown in Dublin in August has been revised upwards to about 1,000.

The revised figure – which is double initial publicly stated estimates – comes as the authorities confirmed a definite line of inquiry was being pursued, and a “case is now being prepared for prosecution”.

A multi-agency investigation led by Inland Fisheries Ireland (IFI) has concluded the final number of fish mortalities is “approximately 1,000, over a distance of around 3.5km”.

A statement issued by IFI in August indicated that the number of fish mortalities recorded in the incident in north Co Dublin was “more than 500, over a distance of 2.1km”.

Documents released under Freedom of Information (FOI) legislation indicate that a member of the public alerted IFI to a fish kill involving multiples of that 500 figure.

Internal documentation logging the call noted: “Caller advised the river is a weird cloudy colour, and thousand (sic) of trout is floating belly up”.

The report also noted “thousands” of dead brown trout as a result of “pollution” were reported by this member of the public to its hotline on Saturday, August 1st.

[ ‘Hundreds’ of fish killed in river Tolka, says Inland Fisheries IrelandOpens in new window ]

Asked to account for the difference in the mortality figures, IFI said the figure of “more than 500” fish killed as mentioned in its August press release was the result of “early investigations”.

“During these events, it can be challenging to reliably estimate the level of impact, as dead fish can flush downstream, sink beneath the surface, get caught in bank-side vegetation, or be picked off by predators.

“And in the aftermath of such events, dead fish may become more noticeable when pollution subsides and the water begins to clarify, or when they start to decompose and rise up from the riverbed due to bloating.

“As the detailed investigation concluded, IFI fishery officers estimated the final number of fish mortalities to be approximately 1,000, over a distance of around 3.5km,” an IFI spokesperson explained.

In August, Green Party leader Roderic O’Gorman blamed the Tolka fish kill on a “substance entering the water”. The cause of the suspected pollution event was not recorded in the correspondence released under FOI, although some sections were redacted.

IFI said the species of fish discovered in the incident included brown trout, eel, stickleback, lamprey and minnow.

[ Detergent firm fined over spill that killed 5,000 fish in TolkaOpens in new window ]

They said the “significant” fish kill triggered the newly enacted national emergency response protocol.

This involved a rapid response team with members from the Environmental Protection Agency, Fingal County Council and the National Parks and Wildlife Service.

“Following a successful multi-agency investigation, led by Inland Fisheries Ireland, there is a definite line of inquiry being pursued, and a case is now being prepared for prosecution,” IFI confirmed.

The organisation thanked the member of the public who reported the fish kill, adding that early notification to its 24/7 hotline (0818 34 74 24) was “essential to help locate a possible cause for any such incidents”.