A popular Hawke's Bay summer swimming hole on the Tutaekuri River has failed a Christmas Eve water quality test after 180,000 litres of effluent was discharged into a connecting stream.
The Land Air Water Aotearoa (Lawa) website said on Tuesday the site, monitored near the Hawke's Bay Expressway bridge, failed the test "due to a pollution incident".
Hawke's Bay Regional Council confirmed there was a significant farm dairy effluent discharge into a tributary of the Mangatutu Stream, which flows into the Tutaekuri River, on Monday.
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The site has temporarily been deemed unsuitable for swimming, and experts recommend people do not swim at this site.
Hawke's Bay Regional Council said the source and cause of the discharge has allegedly been identified and an investigation is under way.
Hawke's Bay District Health Board Medical Officer of Health Rachel Eyre said it was important the public followed the no-swim warning and avoided the Tutaekuri River for at least three days after the Tuesday incident.
The district health board was working with Hawke's Bay Regional Council as it investigated, she said.
Hawke's Bay Federated Farmers president Jim Galloway said it was disappointing to see it happen and says that farmers and others working with waste systems around waterways need to make sure a general upkeep in maintenance is met.
"It can lead from a simple fault or damaged pipe, just look at what happened in Wellington, a simple faulty pipe and it caused all that," Galloway said.
"It's a matter of keeping up general maintenance on your systems and although we don't know the reason behind this discharge I believe the investigation will come out with the proper cause."
Eyre reminded people not to swim in any waterway after heavy rain and to apply the commonsense rule to stay out of the water if you couldn't see your feet in calf-deep water.
Hawke's Bay Regional Council's water quality team will be sampling the water again on December 30 but in the mean time the Lawa status will remain red until a clear result has been received.
Mike Joy, senior researcher at Victoria University's Institute for Governance and Policy Studies, said this is "yet another failure by HBRC".
"If they were doing their job, monitoring and enforcing consent conditions with tough fines this would not happen," he said. "Accidents happen because it is not seen as a priority because of a lax attitude to wastewater spills by HBRC."