Bad water closes beach

Julia Martin and son Ciaran were horrified by news of the water contamination at Mission Bay. Photo / Doug Sherring

One of Auckland's top beaches was closed to swimmers for the first time in a decade last week - but officials are baffled by the cause.

Mission Bay was closed for two days after a February 17 water quality test recorded massive levels of enterococci, a bacteria found in faeces.

Auckland City Council spokesman Grant Ockleston said the city's ageing sewers weren't to blame this time, but there was no way of knowing the reason.

Mission Bay has separated waste and stormwater pipes, and while sewage can still overflow in very heavy rain, that was unlikely in this case, he said.

Signs were put up warning beachgoers the water was unsafe and the test results were listed on the internet, but there was no other publicity.

Mission Bay regular Julia Martin was shocked to learn sewage could overflow into the bay, whatever the cause of last week's incident.

"That's disgusting. I didn't even know there was a stormwater outlet here."

Her mother Colleen Ciobo said the water quality readings should be better publicised. "It's pretty horrific that in a city the size of Auckland they can't get it under control."

The council said it was decided the signs and a web update were adequate given the localised extent of the contamination.

Enterococci levels at Mission Bay on February 17 were 1722 per 100ml of seawater - more than six times the level at which the council warned against swimming.

Two days later the bacteria levels had returned to normal and this week all beaches in Auckland's eastern suburbs had readings of less than 10 per 100ml.

Ockleston said enterococci could occur naturally as a result of seaweed dying off, or from rainfall washing bird and dog faeces into the water.

"We've had areas on Great Barrier that have no human development and have triggered the sample guidelines," he said.

It was another blow for Auckland beachgoers after last year's toxic sea slug scare.

The Mission Bay closure was the fifth at Auckland beaches because of low water quality this summer.

Others were at St Heliers, Blockhouse Bay, Herne Bay and Pt Chevalier.

Cox's Bay, in the west of the city, has a permanent warning against swimming because of ongoing overflows, and is unlikely to be reopened until stormwater pipes are upgraded.

Where sewers and stormwater pipes are combined, heavy rain can wash the sewage through overflow points into the harbour.

As a rule, the council advises not to swim within 48 hours of heavy rain and to stay away from stormwater outlets.

Auckland Mayor John Banks said replacement of the Hobson Bay sewer pipe would almost eliminate sewage overflows in the eastern bays.

But work to upgrade all the city's ageing pipes would take time and investment.

"In a perfect world, it's not good enough," he said. "But it is happening, we need to address it, and it will cost a lot of money.

"We've made a lot of progress, but there is still work unattended and left to be done."