A sewage leak, which Watercare says was caused by someone flushing wet wipes down the toilet, has left the water in an east Auckland creek black and filled with dead fish and eels.
Omaru Creek in Glen Innes was polluted after a sewer pipe started leaking last week.
Patrick O'Meara, chairman of the Tamaki Estuary Protection Society, said he had been to the creek several times to survey the damage and a number of residents had called the society because they were concerned.
"It reeks to high heaven. The water's black. It's pretty sad."
The creek was filled with dead fish and eels, as were surrounding waterways when the Herald visited yesterday.
A Herald Focus and Weekend Herald investigation last month revealed Omaru Creek was one of 41 points around Auckland from which raw sewage often leaked into the harbour.
Watercare staff were at the creek yesterday to clean up the mess, O'Meara said.
"They've got two fire hydrants pumping fresh water into the stream to help flush it and then they're pumping it all out directly into the sewer line."
A member of the public alerted Watercare to the overflow at 2.15pm last Thursday and a crew arrived at Omaru Creek 15 minutes later, said a spokeswoman for the council-controlled organisation.
"Initially, they identified wastewater overflowing from a private property caused by a private blockage. While we are not responsible for fixing overflows on private properties, we cleared this blockage and cleaned the surrounding area as we believed immediate action was required to protect the environment," the spokeswoman said.
During the weekend Watercare found another leak, which the organisation believed was caused by someone flushing wet wipes down the toilet.
"Auckland Council Pollution Response attended and approved flushing of the stream. Auckland Council will be assessing any environmental impact and monitoring."
Temporary signs on banks warn passers-by of the spill and Watercare crews would do more tests today, she said.
However, O'Meara was concerned the polluted water might leach into surrounding waterways, such as the Tamaki Estuary, if it rained.
"If we get a storm or rain or anything [Watercare are] not going to be able to contain it," he said.
The east Auckland leg of the Weet Bix kids' TRYathlon will be held at Pt England Reserve on Sunday. The reserve backs onto Omaru Creek.
Sanitarium spokesman Peter Levett said the company only became aware of the leak when the Herald approached it for comment yesterday.
"Sanitarium treats the health and well-being of our TRYathlon participants and families as top priority, so we have been conducting an investigation.
"We are awaiting the results of some tests, which are due back later this week, so we'll be assessing the situation again before the TRYathlon on Sunday."