KEY POINTS:
Health warning or not, stay out of smelly, discoloured lakes.
That's the message from health authorities after heavy green discoloration affected Lake Rotoehu this week.
There's no health warning on the lake but testing expected to be done this week could change this.
Monitoring of Rotorua's lakes is carried out once a week by Environment Bay of Plenty.
Water sampling is done Mondays or Tuesdays and the results are known later in the week.
If sampling shows algal blooms a warning is usually issued at the end of the week.
Lakes medical officer of health Dr Phil Shoemack warns that if any of the lakes are a funny colour or smell unpleasant, people should stay away from them.
Authorities were alerted to the state of Lake Rotoehu at the weekend after LakesWater Quality Society members Ann and John Green sent the Daily Post a photograph they took of the lake in its pea green state.
Dr Shoemack said it was not possible to monitor the lakes 24 hours a day, seven days a week, so the authorities relied on the public to alert them to potentially unhealthy lakes.
He said Lake Rotoehu was the worst of Rotorua's lakes for algal bloom and it was unusual for Lake Rotoiti to have a health warning in place before Rotoehu.
Warnings are in place for the western bays of Lake Rotoiti affecting Te Weta Bay, Okere Arm and Okawa Bay, and in the Kaituna River at the Trout Pool/Okere Falls and Maungarangi Rd, due to potentially harmful levels of algal blooms of cyanobacteria.
A warning is also in place for Lake Okaro.
Dr Shoemack said algal blooms were common in summer because the warmer weather brought them on.
When they hit Rotoehu they were usually present for months.
Sometimes, however, they could be gone within a few hours which meant it was possible the bloom detected by members of the public at the weekend could be gone by now.
"They can come and go," he said.
Exposure to cyanobacteria, the micro-organism that causes bloom, and its toxins can lead to severe skin rashes and stomach upsets and can spark hayfever and asthma attacks.
