More should be known tomorrow about the high bacteria level reading at Auckland's popular Mission Bay beach.
Auckland Council is performing further tests at the well-loved swimming spot after the detection of high levels of enterococci bacteria, which feed off faeces.
Signs were erected at the beach last night warning that the water was unsafe for swimming, but some people still took to the water today.
Auckland Council acting chief operating officer Ian Maxwell said the results were from regular weekly water quality testing, carried out at all of Auckland's 63 beaches.
A council spokesman said tests from Mission Bay were the only ones which came up positive - with results from neighbouring beaches at Kohimarama and St Heliers being of no concern.
Further tests were being carried out to confirm what the cause of the high bacteria level was.
The spokesman also said the test result had been a surprise _ given Mission Bay normally had no water quality problems.
"There's a whole range of possible causes. It could be a whole lot of dog poo washed up somewhere, it could be a dead animal's carcass floating by, it could be a bag of stinking old nappies that someone's dumped overboard, it could be someone flushing out the waste system on their boat,'' he said.
The result could also have been from a false positive, Mr Maxwell said.
He advised people to stay out of the water at Mission Bay in the meantime.
"This result is surprising. Checks of the wastewater and stormwater network do not indicate a network problem and there have been no reports of overflows.''
Further test results were expected to be available tomorrow afternoon.