Hallett's Bay - a popular swimming spot in Lake Taupō - has tested positive for a toxin-producing algae species.
It's the sixth area to have this strain of algae - one that has never been seen before in Lake Taupō.
The algal mat was triggered by still, warm conditions and the presence of nitrogen and phosphorous in the water.
People have been warned that even wading up to their ankles in the water could cause illness - including eye irritation, breathing difficulties if inhaled, and in more severe cases, muscle numbness and tingling.
Dogs can be particularly vulnerable if they come into contact with the water.
While the species is known to produce harmful toxins, whether it is or not in Lake Taupō is still being tested by NIWA scientists. Those results are expected to be known over the next few days.
The known affected areas so far are Five Mile Bay, Acacia Bay, the main lakefront in Taupō, Whakaipo Bay, Kinloch Beach, and now Hallett's Bay.
Meanwhile, Taupō District Council has reinstated its water intakes at the lakeside settlements of Hatepe and Motuoapa, which were turned off as a precautionary measure on Friday.
Operational services group manager Kevin Strongman said they will continue to take a cautious approach.
"We will be undertaking testing twice a week for the next month or so to err on the side of caution. This is above what our emergency plans require us to undertake but the health of our community comes first and foremost."
Newshub.
