Poorly managed or maintained septic tanks are being blamed for high levels of E coli recorded in lagoons at Piha and Karekare.
The waterways have been regularly declared unsafe for swimming this summer by Auckland Council after test results indicating contamination by human faeces or animal sources.
The council's Safeswim programme monitors the water quality of beaches and freshwater lakes and rivers across the region with regular testing between November and March.
Warning signs are put up if high levels of E coli are discovered.
The Karekare and Piha lagoons have been tested over 10 weeks since November 2013. Results show there were five amber and three red alerts requiring action at the two Karekare lagoons.
The two Piha lagoons produced four amber and five red alerts. Overall results show levels as low as less than 10 E coli/100ml and as high as 5200 E coli/100ml.
Waitakere Ranges Local Board chairwoman Sandra Coney says water run-off from malfunctioning septic tanks was picked up last year as a reason for the contaminated water at Piha.
"One of the things that has exacerbated the problem is the sand build-up along the coast. The water is staying trapped in the lagoons which doesn't help," she says.
Ms Coney says septic tanks from private properties are most likely the culprits and says residents pay to get the tanks inspected every three years.
"It's going to take the whole community to get behind this and see it's a problem affecting everyone.
"It's a blot on the quality of the place and it's completely unacceptable in places where throngs of people swim in the summer."
Piha Ratepayers and Residents president Ken Cowan says the group has written to the council to request urgent action be taken.
Council land and water management team leader Phil Brown says testing indicates human and animals as sources of contamination.
"This could be consistent with contamination from poorly managed or maintained septic systems.
"Council is currently undertaking further sampling through the catchments to try to further isolate where these issues are originating from."
He says the council wants to work with residents to ensure septic tanks are maintained and managed effectively.
"The busy holiday period sees a large influx of people into these holiday spots and this puts a lot of pressure on septic systems, sometimes leading to them overflowing or otherwise failing."
He says minimising water use will reduce the pressure on septic tanks and says they should also be well maintained before and after visits by large groups.
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