Auckland Mayor Phil Goff is promising wastewater overflow will be cut by 90 per cent within a decade, as faecal contamination makes some city beaches unswimmable.
Seven Sharp reported this happens because of a century-old combined stormwater and sewerage system in some parts of the city.
Heavy rain pours stormwater into the sewerage system, causing the manholes to pop.
"Because the pressure is so great, they pop," environmentalist Liz Walker said.
Upstream from the beaches, at Meola Creek, an incredible volume of water taxes the maxed-out system.
"We have condoms, we have human faeces, we have tampons," Ms Walker said.
Mr Goff admitted there's faecal contamination but outlined a variety of responses being implemented.
Signs put up under the Safeswim program tell beachgoers if a beach is safe or not.
In terms of infrastructure, limited separation of sewerage and stormwater is being put in place.
And a $1 billion-plus central interceptor will collect stormwater and sewerage and send it to Mangere for treatment.
"We can knock back by 90 per cent the amount of wastewater overflow within one decade. We're committed to doing that. We will deliver for Auckland," the mayor said.
And beach contamination isn't just an Auckland problem.
"You'll find that there are many ageing infrastructure systems around the country that simply aren't coping." Mr Goff said.
St Mary's Bay is one of many inner-city Auckland beaches that have been unswimmable.
St Mary's Bay Residents Association's David Abbott said faecal contamination of the seawater is "completely unacceptable".