Illegal or poorly maintained private sewage and stormwater pipes are being blamed for the large amount of human waste polluting Auckland beaches.
Sewage overflow is an ongoing problem for the city and Auckland Council DNA has been testing about 20 beaches, known to have water quality issues, over the past four years.
Nearly 650 samples were taken and more than half of those showed human sewage contamination.
Ageing wastewater infrastructure has been blamed for the overflow in the past but Anin Nama from Watercare said that was wrong.
"The sources that we've identified to date predominantly tend to be related to people that have cross connected their wastewater to the stormwater, private pipes that have a tendency to fail and leak over time," he said.
"We've got nothing that indicates that Watercare's infrastructure is inadequate."
Mr Nama said their findings from Takapuna Beach are a good example.
"We've identified a toilet block in their private pipes... actually leaching wastewater and entering into the stormwater system and then onto the beach," he said.
"So you know, the positive result that was identified from Takapuna was a direct result of poor private infrastructure and not ageing infrastructure from Watercare."
He said people disposing fats, oils or wetwipes down into sewage systems also causes blockages.
That too, can lead to overflow problems.
Mr Nama said Watercare can only do so much.
"If we continually say, 'It's a Watercare issue, it's a Watercare issue', we will not solve the problem," he said.
"[The] majority of the problem will be associated with stuff that should not be getting into our network that is getting into our network by people putting things down."
Nick Vigar from the council's Safeswim branch, which looks at water testing, encouraged anyone with suspected pipe leakages to get in touch.
"There's a fair degree of expense in trying to track these problems," he said.
"We're more than happy if people will come to us and say, 'look, we think there's an issue', absolutely we'll help and resolve that issue with them."
Mr Vigar said the public should make sure they check the Safeswim website, which shows the water quality at beaches, before they go swimming.
He said council has been working hard on identifying and fixing the wastewater issues but it would not be a quick fix.