Hot summer poses algae threat for lake
Swimming in Lake Taupo¯ could be off limits this summer if a dangerous algae growing in the shallows doesn’t clear.
Waikato Regional Council scientists have identified a potentially toxic algal species called phormidium growing inside algae near the lake shore.
And experts say it could be here to stay if the recent spate of hot weather continues.
The discovery has already impacted the Taupo Ironman 70.3 planned for this weekend with the swimming leg dropped from the event and is now a run-bike-run event to prevent athletes coming into contact with the material.
The lake last experienced an algal bloom in 2003. However, this was the first time the cyanobacteria phormidium had been found.
It is thought to be flourishing because of the unusually hot and still December weather, the scientists say.
Dr Neil de Wet, medical officer of health for Toi Te Ora Public Health, said contact with the algal mats could cause rashes on the skin and stomach upsets.
‘‘It produces neurotoxins so there can be more severe effects, such as tingling, numbing and difficulties breathing,’’ he said.
Signs went up yesterday telling holidaymakers and locals to stay out of the lake and to keep their dogs out too.
Waikato Regional Council water scientist Dr Eloise Ryan said the browny-green algae mats were forming on the lake bed in shallow areas.
‘‘It’s not like a typical algal bloom that you usually see floating on the surface. It’s easily dislodged when walking through it,’’ she said.
‘‘You’ll also see floating greenbrown blobs, in the water.’’
De Wet said material could easily wash up on shore.
‘‘It’s really important to keep young children away from the shoreline because there can be quite dense mats of algal on the shore’’.
Ryan said it was difficult to predict how long the bloom would persist.
‘‘If we continue to have long dry periods, it will continue to grow.
‘‘We would need quite significant rain and colder periods. I see those are predicted in the coming weeks. So, if the weather does change, that will slow the growth of the algae.’’
These kinds of algal blooms tended not to entirely disappear, she said.
‘‘We may see the bloom lessen, but if these conditions persist over summer, we could see the recurrence of this bloom, going forward, over summer.’’
Samples had been taken at five locations near Taupo¯ township: Five Mile Bay, Acacia Bay, the main lake front in Taupo¯ , Whakaipo Bay and Kinloch Beach. Samples from the lake’s southern end were being collected yesterday.
De Wet said it would be wise to treat all areas of the lake with caution.
‘‘Our advice would be for the public to be aware and to look before using the lake.
‘‘If there’s any algal material or any strange odour, it’s best not to use the lake, if in doubt.’’
Ryan said it was not known whether the phormidium was producing toxins at this stage.
‘‘At any time, it could turn toxic, so we’ll be continuing to monitor this regularly,’’ she said.
NIWA and Cawthron Institute scientists would analyse the samples and return a verdict on Monday, she said. Swimming in rivers was safe, Ryan said.
‘‘It doesn’t like rapidly flowing water, as it grows in still water.’’
De Wet said Taupo¯ doctors had not passed on any reports of people suffering ill health effects from the algae.
Taupo District Council’s Kevin Strongman said Taupo¯ ’s water supply was still safe to drink.
The council had comprehensive monitoring to ensure no algal matter was present near the water inlets and it was increasing the frequency of its testing, he said.
Any algae passing through the Huka Falls would be dispersed and destroyed, so there was no risk to water supplies further down the Waikato River, Ryan said.
Members of the public who notice algal blooms in other areas around Lake Taupo¯ can report them to the regional council on 0800 800 401.
For health advice, people should call the Healthline on 0800 611 116. For advice on drinking water and beach access call the district council on 0800 ASK TDC (0800 275 832).