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Bacteria levels at an inner city swimming beach have spiked to more than eight times the safe level, in a week when scorching weather sent many people to the waters to cool off.

Judges Bay on Auckland's Tamaki Drive was closed to swimmers yesterday after a routine test found unsafe levels of enterococci bacteria.

The finding sparked new debate about how the council plans to clean up its beaches. Supporters of a speedy $5 million upgrade to the beach claim the bacteria surge proves how urgently work is needed. But opponents say other city beaches need cleaning up just as quickly.

Council testing found bacteria levels of 2359 enterococci per 100ml of seawater on Wednesday - more than eight times the safe swimming limit of 280 per 100ml.

Auckland City Council environmental health manager Chris Dee said that did not mean there was eight times as much risk of getting sick.

He said enterococci could indicate there was sewage in the water, but it was not always from human waste.

Mr Dee said city beaches were always risky for swimming when it rained after a dry spell and "that's why we always say don't swim for 48 hours after heavy rain".

More bacteria tended to gather in Judges Bay because it was small and had a slim outlet to the ocean, he said.

Auckland City Council tests water at 20 popular beaches every week over summer - 13 in the city, four on Waiheke and three on Great Barrier Island. Bacteria levels are usually well within safe limits. Only one other beach - Pah Beach on Great Barrier Island - has tested above 2000 enterococci per 100ml seawater in the past year.

Enterococci are commonly found in the human intestine. Significant levels in water can indicate a higher than usual level of sewage pollution.

Councillor Aaron Bhatnagar, whose Hobson ward includes Judges Bay, said this week's swimming ban proved he was right to push for sewerage upgrades. He and other councillors from the Citizens and Ratepayers party were criticised when they voted for an upgrade in the wealthy Hobson area at the same time they voted to slash $80 million that would have been spent on sewerage upgrades at other beaches.

Some of the beaches that will be upgraded more slowly under planned spending cuts - Mission Bay, Kohimarama and St Heliers - were closed this week after power cuts caused a spill of raw sewage.

Yesterday, Western Bays councillor Graeme Easte said upgrades at Judges Bay should not go ahead of other beaches. He said Coxs Bay in Westmere had been on the "clean up list" since the 1980s.