Bacteria alert at beaches

Sisters Anna Hemphill and Vicks Hemphill said they wouldn't have gone in the water at Mission bay if they'd known the danger. Photo / Doug Sherring

Officials are under fire for failing to test water at Auckland beaches likely to have been polluted by last weekend's storms.

Heavy rain and king tides meant many beaches were contaminated with wastewater and stormwater runoff.

Pre-planned tests at western beaches on Monday revealed 80 per cent were unsafe for swimming. Bacteria levels at some were more than 70 times the maximum safe amount.

Samples from other beaches later in the week showed lower levels of bacteria as the problems subsided.

But Auckland Council stormwater manager Grant Ockleston admitted it was "most likely" people had been swimming in contaminated water at untested beaches at the start of the week.

Bacteria enters the sea in three ways:

* Heavy rainfall can overwhelm the water network, causing waste and stormwater to mix and flow into the sea at purpose-built "relief points";

* Toxins leach into stormwater;

* Waste flows into the sea on floodwater or king tides.

The council tests 52 beaches each week between November 1 and April 30. Samples are taken in batches by area and results are posted on the council website.

North Shore sites are no longer tested because the now-defunct North Shore City Council deemed it unnecessary after years of good results.

The amount of enterococci bacteria - which indicates the levels of other bacteria - are used to determine whether the water is safe.

Terrey Fitzgerald, who manages council-contracted testing company Aqualab, says red, amber and green alerts are used to signify the severity of the problem.

More than 280 enterococci bacteria per 100ml generates a red alert. Some beaches tested on Monday had counts of 10,000.

Fitzgerald would have preferred more checks after last weekend's flooding.

"As a beachgoer I think they should have been testing whether the beaches were safe earlier in the week."

And beachgoers at Mission Bay - which wasn't tested until Tuesday - were concerned by the lack of warning.

Sisters Vicks and Anna Hemphill, who arrived from London after the storm, said they "wouldn't have gone in" if they'd known the danger.

Resident Ross Duder said the council should put up more warning signs.

"There is one sign but I don't think visitors see it. They should put them on the sand."

Ockleston said unscheduled tests after heavy rain were too expensive because most sampling was done by helicopter.

"There's only so much data collection we can do because we have to balance all of the costs of doing this sort of thing."

Council officers were last night testing water from six of Auckland's most popular beaches.

Signs went up at Blockhouse Bay, Kohimarama, Mission Bay, Okahu Bay, Pt Chevalier and St Heliers Bay warning swimmers of possible contamination.

That came after Friday's torrential rain overran the stormwater system, causing it to overflow into the sewerage system and be pumped into the harbour.

Auckland Council spokesman John Evans said he did not know if the urgent tests were a result of Herald on Sunday inquiries about the issue earlier in the week.

Ockleston said people should avoid swimming in the sea for up to 48 hours after heavy rain because of the possibility of contamination.