Swimmers have been warned off one of Auckland's most famous city beaches because of high levels of bacteria.
Warning signs have been put up at Mission Bay telling swimmers and beach-users of the poor water quality.
The contamination was discovered yesterday by Auckland Council's Safeswim monitoring programme, which tests water quality weekly at 63 Auckland beaches.
"Our advice is for people not to swim at Mission Bay on Thursday and Friday," acting chief operating officer Ian Maxwell said.
"Our testing indicates ... levels of bacteria [that] suggest a potential risk to human health."
The test result has surprised the council because checks of the wastewater and stormwater networks did not indicate a problem, and no overflows had been reported.
"This may be a one-off incident from an animal source, a boat dumping, or a false positive," Maxwell said.
He encouraged beach-users to swim at other local beaches including nearby Kohimarama and St Heliers.
The beach's status was today already beginning to affect businesses that rely on access to the water.
Mission Bay Water Sports, that runs paddle boarding and kayak tours at the beach has been forced to close while health warnings are in place and is not sure when it will next open.
"It is certainly not good for us," manager, Rebecca Paley-Williams said.
"It is hard to say what the effects will be but the first priority is client safety."
The company can get up to 200 clients per day, but today there were none.
"We are certainly hoping that whatever needs to be fixed is fixed," she said.
"It's just something we need to wait out."
Despite a gloomy day a number of people had come down to Mission Bay for a swim.
A group of St Peters College students on school holiday were forced to swim in the fountain instead.
However, some people had not seen the signs and had made their way into the affected water.
Water quality in Auckland's bathing beaches and lakes is usually good and meets New Zealand health guidelines, the council said.
More tests will be carried out on Friday to assess Mission Bay's safety.
- Fairfax Media