Popular Takapuna Beach yesterday became the latest of many Auckland coastal swimming spots affected by pollution. Science reporter Jamie Morton looks at five questions many sun-seekers will be asking.

1. What Auckland beaches are currently out of action?

A quick glance at Auckland Council's Safeswim website will show a concerning number of local beaches aren't safe for swimming.

Sixteen spots around the region are subject to "permanent" warnings by Auckland Council's official Safeswim monitoring website because of ongoing water quality problems.

Those are Cox's Bay, Meola Reef, Weymouth Beach, Little Oneroa Lagoon, Wairau Outlet, Piha Lagoon, North Piha Lagoon, Te Henga (Bethells) Lagoons, Laingholm Beach, Wood Bay, Taumanu East, Green Bay, Clarks Beach, Titirangi Beach, Fosters Bay and Armour Bay.


But 11 others have temporary "high risk" warnings in place - those are Long Bay, Waiake Bay, Browns Bay, Mairangi Bay, Milford, Milford South, Takapuna, Narrow Neck, St Mary's Bay, Judges Bay and Christmas Beach.

Others - including Maraetai Beach, Cockle Bay, Mellons Bay, Bucklands, Herne Bay, Home Bay, Point Chevalier, Waikowhai Bay, Sandy Bay and Oneroa - were considered "fair".

These warnings can change as new test results come in.

Beaches with high risk statuses mean people are exposed to a moderate to high risk of infection with contact with the water, making it unsafe for swimming, while those with "fair" gradings carry a low to moderate risk.

That means the beach's water quality still meets an unacceptable standard for swimming, but council officers need to investigate, and some people at high risk of infection - the very young and the very old - should be especially cautious.

The rest of Auckland's beaches currently have good water quality, and open ocean sites were typically better than urban ones.

"There are two reasons for that," Safeswim technical lead Martin Neale explained.

"One is urban areas have more potential sources of contamination and the other is that open ocean systems get much more flushed by tidal cycles."

2. Why are there so many warnings at the moment?

Much of the current warnings can be put down to recent rains driving more diffuse pollution into the ocean.

The animation in this article shows the predicted changes in bacteria concentration during a rain event in Auckland.

Big rainfalls - like those which hit yesterday and those forecast for this week - can mean wastewater networks become overwhelmed by stormwater and groundwater, leading to sewage overflows.

Wet weather events also carry a "first flush" of stormwater runoff, which can be laden with solid and dissolved contaminants, such as litter and animal faeces.

The effects of these are worse after long dry spells - such as those as we've just experienced.

There are also more warnings in place than previous summers because Auckland Council recently upgraded its programme from previous national guidelines to meet international best practice.

The new upgraded programme now provides real-time information about water safety and quality together with public health alerts at 84 of Auckland's beaches this summer.

"We've done some testing, and typically, if we get an overflow alert from the network, the website is updated within 10 minutes," Neale said.

"The tagline we are running this summer is check before you swim."

3. What might happen if I did swim in contaminated water?

Most water quality problems at Auckland's beaches stem from animal or human faeces, which can foul water with disease-causing bacteria, viruses and nasty bugs like salmonella, campylobacter and giardia.

Lifeguard Dan Lee stands with a sign at Takapuna Beach warning people of the water quality on the beach. Photo / Dean Purcell
Lifeguard Dan Lee stands with a sign at Takapuna Beach warning people of the water quality on the beach. Photo / Dean Purcell

The most common illnesses caused include gastroenteritis, respiratory illnesses or ear, eye and skin infections.

READ MORE: NZ's best and worst swimming spots revealed in new website

Council staff constantly test for current and projected future levels test for levels of enterococci bacteria, which indicates the presence of faecal matter when it occurs in high levels.

If you are exposed to bad water quality, you might become sick, usually within three days of swimming.

Anyone experiencing symptoms of water-borne illnesses should phone Healthline on 0800 611 116.

4. Where is the pollution coming from?

Often, it can be blockages in wastewater pipes caused by roots, fats, rags or other objects like ropes, concrete, toys and bricks.

In some cases, natural groundwater may come into contact with human or animal faecal matter before entering stormwater pipes or natural waterways discharging to the coast.

But, again, one of the main risks to bathing beach water quality occurs during heavy rainfall.

This was a particular problem in old combined pipe networks such as those that still operate around the suburbs of Grey Lynn, Ponsonby, Herne Bay, Freemans Bay, St Mary's Bay, Waterview, Westmere, Sandringham, Avondale, Point Chevalier and Arch Hill.

Wet weather wastewater overflows have historically discharged into local waterways after heavy rain, and such old networks still service up to 15,000 households in central Auckland.

Despite the presence of combined sewers, the majority of Auckland was serviced by separated stormwater and wastewater pipes.

Visitors at Piha Beach have often ignored warnings about poor water quality at Piha Lagoon. Photo / File
Visitors at Piha Beach have often ignored warnings about poor water quality at Piha Lagoon. Photo / File

During dry weather, there were typically few problems within these networks, but with heavy rain, some wastewater pipes received inflow and infiltration of stormwater and ground water.

These came from defects such as low gully traps, unauthorised cross connections, roots and cracks in pipes.

A wastewater pipe could quickly become overwhelmed if too much water entered - and one house-lot of stormwater illegally connected to the wastewater network could displace more than 40 house-lots of wastewater.

When wastewater pipes were overwhelmed, they typically discharged diluted wastewater from overflow points engineered to prevent major damage to infrastructure, into local waterways, the stormwater network or directly to the coast.

5. What's being done about it?

Auckland Mayor Phil Goff has acknowledged the situation isn't acceptable.

Current planning and investment levels in our stormwater and wastewater systems meant poor water quality would persist for 30 years.

One of the biggest problems was in the Western Isthmus, where more than 70 outfalls overflowed into the Waitemata between 25 and 60 times a year.

But with the right level of investment, Goff wrote in an opinion piece for the Herald, the council could clean up beaches and harbours within a decade, reducing wastewater overflows by as much as 80 to 90 per cent.

The council group was making a capital investment of $6 billion over the next 20 years to improve water infrastructure.

Over the next 10 years, the council will be spending $700 million on stormwater, while Watercare will be investing $2.8b in new wastewater infrastructure, with a further $3.1b in the following decade.

The council will also soon start building a $960m system called the Central Interceptor, which will reduce the frequency of wastewater overflows to waterways and beaches, and will be supported by other major new infrastructure projects.

Performance standards for wastewater networks have been tightened under the new Auckland Unitary Plan, and a new Auckland-wide bylaw has been adopted for stormwater management.