Uisce Éireann has been fined €3,500 in relation to a chemical spill in north Cork that led to a major fish kill in the River Allow.
The case was taken by Inland Fisheries Ireland (IFI) against the water utility company.
In a statement, IFI said it welcomed the conviction, describing the incident as "an entirely avoidable ecological disaster for a sensitive river habitat" that effectively sterilised an 8km stretch of the river and "may take years to recover".
At Mallow District Court, Uisce Éireann pleaded guilty to one charge under the Fisheries (Consolidation) Act 1959 of permitting or causing deleterious matter to fall into the river's waters.
Judge Colm Roberts imposed the €3,500 fine and costs of €3,267.
The court was told the incident happened on or shortly before Sunday 9 June last.
IFI Senior Environmental Officer Andrew Gillespie told the court that he was called to the Freemount Water Treatment Plant by Cork County Council staff following a chemical spill into the River Allow, a tributary of the River Blackwater, and an important spawning ground and nursery for salmon and trout.
He said that when he arrived, a major clean up was under way.
Mr Gillespie said that a pipe running from a 13-cubic metre tank of polyaluminium chloride - an acidic solution used in the water treatment process - had failed and the chemical had entered the river via an adjacent drain.
The tank, he said, had about three-cubic metres of the chemical in it at the time, most of which had leaked out.
Mr Gillespie said an investigation determined that the chemical spill had affected an 8km strech of the River Allow over an area of 40,000sq/m.
It was very difficult to determine the total number of fish killed, he said, but it was certainly in the "tens of thousands" based on a "conservative estimate" of one fish killed for every 2sq/m of river affected.
"All we can say is that there were no dead fish upstream and there were no live fish downstream for 8km," Mr Gillespie said.
As well as juvenile and large salmonids, large numbers of dead and dying lamprey were also observed, a fish that normally stays on the river bed.
Mr Gillespie said the water quality returned to normal within days, but the age and class distribution of the fish populations could take several years to return to the way they were.
BL for Uisce Éireann Aoife Sheehan said her client had been fully cooperative and had informed all relevant authorities as soon as the leak was discovered.
She said the company pleaded guilty and had taken immediate remedial steps as soon as the spill was detected.
The scale of the response, Ms Sheehan said, reflected how seriously Uisce Éireann took such matters and the event had had an impact on national policy regarding chemical storage.
She told the court that the storage tank in question was fully bonded, but investigations indicated that a pipe leading from it had been subject to a build-up of heat that caused it to disintegrate, causing the leak.
It was believed a valve had not opened while a pump was in operation, she said, which led to the temperature increase.
Ms Sheehan said that a task force had been established to look at national policy to ensure a similar situation does not occur.
She added that the water supply from the Freemont plant serves a population of 3,000 people and this was not compromised as a result of the leak.
Judge Colm Roberts said he appreciated that Uisce Éireann may not have the funding to carry out all of the works it would like to, but he said it was a "real concern" that the plant was audited before the leak occured.
"It's to do with having the right plan and the right maintenance. They stepped up to the plate, but it was really a case of closing the stable door.
"It is often the simple things that don't get done when you are dealing with organisational pressure," he said.
The court heard that Uisce Éireann had not been previously prosecuted in relation to the Freemount plant, but there had been 18 cases for "similar incidents" between 2015 and 2024, and a number of prosecutions were pending.
Judge Roberts said he was taking into consideration the guilty plea, the works in progress, and the "legacy issues".
He convicted and fined Uisce Éireann €3,500 - giving it one month to pay - and ordered the company to pay €3,267 in legal costs.
