Emma Stanford, senior reporter

Another bout of sewage spilling into popular beaches on Auckland's North Shore has the community concerned.

Castor Bay, Wairau Outlet and Milford Beach are under a 'do not swim' notice until 5pm Friday because of wastewater contamination.

As at 5.26pm on Wednesday, the wastewater overflow sensor reading showed a very high risk.

When RNZ visited each site, there were no physical signs telling people of the risk, just black markers on the Safeswim website.

Castor Bay Ratepayers and Residents Association president Hamish Anderson said it was frustrating and happening too often, through dry and wet weather.

"It's inconvenient for locals and visitors to our beautiful beach. It's resulting in further degradation of the Hauraki Gulf and it's just not a good look for our clean, green brand."

He wanted better communication from Watercare, after only hearing about it through the media on Thursday morning.

"It's kind of crazy that they seem to rely on people checking the Safeswim website to see if it's safe to enter the water at our beaches," Anderson said.

"When, in the case of contamination, they should be putting signage up so people go to the beach and clearly see it is unsafe. Most people don't check Safeswim before they go to the beach."

Castor Bay on Auckland's North Shore. Photo: RNZ / Emma Stanford

Andy Parker from the Castor Bay Swim Rise group said they still went for their daily dip on Thursday morning after checking Safeswim.

"Everyone discussed it and we looked at the water and there was certainly no sign of anything untoward. I actually don't stick my head under, a lot of people don't, just because it's become too unreliable, I think."

Parker said when the water looked dodgy, the group usually moved up to Campbells Bay.

North Shore ward councillor Richard Hills said signs were normally put up if the issue was expected to last a few days.

"Because there are so many beaches and often issues pop up randomly in dry weather, but usually in wet weather, it's far easier for everyone if it's about checking the website.

"Obviously signage would be, in my opinion, appropriate if it is something that's going to last longer than 24 hours, so I'll be asking those questions once I know exactly what the issue is."

Castor Bay on Auckland's North Shore. Photo: RNZ / Emma Stanford

Watercare said the overflow was caused by a blockage and crews were flushing the pipe and investigating.

It said blockages could often be caused by 'fatbergs' - a combination of fats, oils and grease mixed with things like wipes and rags.

Wet wipes made up 70 percent of overflows across Auckland, Hills said.

"Often it's about all of us trying to prevent sticking wet wipes and fats and other greases down the pipes."

Watercare said there was nothing to suggest there was an ongoing issue in the area, but it encouraged beachgoers to check the Safeswim website before heading out this summer.

Te Whatu Ora medical officer of health Dr David Sinclair said if there was a red or black pin showing over a beach on the website, people should stay out of the water to avoid gastroenteritis or skin, ear or eye infections.

If you get sick after swimming, you can call Healthline on 0800 611 116 for advice, or contact your doctor.

Sinclair also advised people not to collect shellfish from anywhere within the Waitematā Harbour.

Any fish taken from there should be properly cleaned, gutted and cooked.

This story was originally published by RNZ