Northern Ireland Water has been fined thousands of pounds after blood and toxic sewage leaked into the River Foyle.
The “poisonous, noxious and polluting” discharge was found to have entered the Foyle from a combined sewer network at Lisahally a year ago.
NI Water pleaded guilty to causing waste to enter the river and was fined £3,500 plus £331 costs last week in Londonderry.
It has now emerged that during the incident on March 1, 2011, “deleterious” harmful matter entered the river.
Derry Magistrates Court heard that the leakage, believed to have been from a local factory, also contained blood.
A solicitor acting for the Loughs Agency said the level of discharge was so high that the blockage had to be cleared from the Strathfoyle pumping station.
The discharge was described as “putrid smelling” and having the potential to impact negatively on fish in the River Foyle.
NI Water's solicitor said nothing of this nature had occurred before and that the blockage was cleared in “three-and-a-half to four hours”.
He told the court that the company believed the incident occurred following “excessive amounts of discharge” from the factory.
The solicitor stressed that NI Water knew nothing of the blockage until it was reported to them.
“Thankfully no fish were killed,” he said.
District Judge Barney McElholm said at the hearing: “NI Water should put into place arrangements so if this happens again it can be dealt with more quickly.”
A spokeswoman for NI Water said: “This pollution incident was caused by a blockage in the sewer combined with an increased discharge from a local factory.
“NI Water staff were on the scene and had cleared the blockage within three hours of being notified of the incident.
“NI Water takes any issue of pollution extremely seriously and has invested approximately £490m over the last three years to bring the sewerage network and waste water treatment works up to an acceptable standard.
“NI Water, however, is asking for the public’s assistance to help reduce these occurrences by not placing inappropriate items in the toilet, down a drain or into the sewers.”
Just last week the Loughs Agency spoke about major efforts to reverse rapidly declining Atlantic salmon stocks in the Foyle.
Chief executive of the agency, Derick Anderson, said there were 134 commercial and agricultural pollution incidents along the river system last year, a number of which were progressing to court.