NORTHERN Ireland Water is "presiding over a broken system" and must be held accountable, environmentalists have said.
The comments by Friends of the Earth director James Orr came after the public body admitted responsibility for a pollution leak which killed more than 1,600 fish in a Co Down river at the weekend.
It is the third major fish kill caused by leaks from their sewage plants in the past three years.
NI Water said the pollution, which affected the Annsborough and the Carrigs River on Saturday was “due to an accidental discharge of polyelectrolyte”, from the neighbouring Annsborough Waste Water Treatment Works.
The discharge is believed to have been caused by a damaged pipe.
The major fish kill in Co Down is the third directly caused by the firm's wastewater assets in the past three years.
It follows an incident at Killyclogher, Co Tyrone in June 2014 and one in Mallusk, Co Antrim in September 2015, which is currently the subject of legal proceedings.
NI Water manages and maintains more than 1,000 wastewater treatment works and more than 1,200 wastewater pumping stations.
When asked if any staff had been disciplined for their role in causing the harmful pollutants to be discharged into the water supply NI Water deemed that "no disciplinary action was appropriate".
"Full investigations of the previous two incidents found the pollution was as a result of technical issues and no disciplinary action was appropriate," a spokesman said.
Mr Orr said the response of NI Water to the pollution is "unacceptable" and said the body was presiding over "a broken system".
"Ultimately because of the endemic and systemic nature of their pollution this has to be an issue for their chief executive and their board.
"They need to take responsibility. These are not isolated incidents...they suggest they are incapable of taking them seriously."
SDLP South Down MP Margaret Ritchie has called for an immediate investigation into problems at the Annsborough waste water treatment works.
"The representative from NI Water has just asserted that problems with pipework have emerged at this Waste Water Treatment Works in Annesborough – there is no reference to the scale of those problems," she said
"What is patently clear is that NI Water needs to immediately carry out a proper and adequate investigation into the nature of the problems with the pipework at the Waste Water Treatment Works; identify funding and carry out immediate works to replace or repair the problems which caused the chemical leak into our important river drainage system," she added.
