More than 150 eels were killed when pollution escaped into a Co Down river from a sewage pumping station, Bangor Magistrates Court has heard.
Northern Ireland Water was fined £2,000 plus costs after admitting the discharge from Cherrymount sewage pumping station, Bangor, in May 2011, the Department of the Environment said in a statement.
A DoE spokesman said that a water quality inspector acting on behalf of the Northern Ireland Environment Agency inspected the Ballyholme River near to the pumping station on May 16, 2011.
The river was found to be heavily impacted with sewage fungus, the water was running discoloured and there was sewage sludge on the river bed.
"Some 1,200m of waterway was adversely affected", the spokesman added.
Northern Ireland Water said that the pollution incident had been caused by a technical failure, which resulted in the alarm not working effectively and not alerting the contractors responsible for the site when a problem arose.