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Published: 2017-12-07 20:15:00

Dense mats of potentially toxic algal species have been found at five sites around Lake Taupō, prompting a warning for the public to avoid swimming in affected areas and any contact with algae blooms that may be on shore.

After receiving reports from the public of algae blooms, Waikato Regional Council scientists collected a number of algae samples on Tuesday and again yesterday from five sites.

Testing overnight by NIWA scientists has confirmed the presence of potentially toxic algal species, including Phormidium, at areas within Five Mile Bay, Acacia Bay, the main lake front in Taupō, Whakaipo Bay and Kinloch Beach.

Regional council water scientist, Dr Eloise Ryan, said: “The algae blooms are generally in water from the height of the ankle and up to the waist. However, they will shift depending on water flows and wind, so we’ll continue to test and monitor these areas.

“It was windy when we collected samples at the lake yesterday, which helped to disperse the algae blooms. But we’ve had reports from our Taupō-based staff of dense mats forming in the calmer conditions today.”

Dr Ryan added, “The good news is that temperatures are signalled to lower during the day and overnight, and rain combined with the predicted wind may help to slow the algal growth and disperse future blooms.”

Based on the test results to date, Toi Te Ora Public Health, Medical Officer of Health, Dr Neil de Wet, has issued a health warning. People are advised not to paddle, wade, swim, or participate in any recreational activity that might involve any direct contact with the algal mats or swallowing of affected lake water. Parents should ensure young children do not come into contact with algal mats in the water or on the shoreline.

Dogs are especially vulnerable, so people should keep their pets and livestock out of the water and off the shoreline in the known affected areas or where the algae is visible.

Dr de Wet said, “Contact with algal mats can cause symptoms such as skin rashes, stomach upsets and respiratory symptoms such as triggering of asthmatic attacks. If material from algal mats is swallowed it can cause neurological symptoms such as numbness and weakness, visual symptoms and, in severe case, affect the ability to breathe.

“The algal mats can come free and accumulate on the shoreline or float on the surface. While there are five areas currently known to be affected, due to the weather conditions the blooms could disperse or occur in other areas of the lake, so the community should be vigilant and check for signs of algal mats before entering the water in other areas,” he said.

Toxic algal species often multiply to high levels during periods of warm, sunny weather. In lakes they can form extensive green to black-coloured mats that settle on rocks and the lake floor. Significant clumps sometimes break off and float free, collecting on the water's edge.

Topia Rameka, CEO of the Tūwharetoa Māori Trust Board said, “Taupō Moana is a dynamic ecosystem and the last algal bloom event we experienced was in 2003 – the priority now, as it was then, is the safety and welfare of our community.”

With the Ironman 70.3 Taupō being held this weekend, organisers are being made aware of the warning issued today.

Meanwhile, Taupō District Council has comprehensive monitoring in place to ensure the quality and safety of drinking water at all times.

There is currently NO risk to the water supply and the frequency of testing at water intakes will be increased as a precaution until the situation resolves.

Waikato Regional Council monitors the waterways throughout the year, but the frequency increases to weekly in summer as the potential for an occurrence of algae blooms grows. While algal blooms occur naturally in hot and sunny weather, they also depend on other factors, such as the amount of available plant nutrients, phosphorus and nitrogen within a lake.

Members of the public who notice algal blooms in other areas 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).

Phormidium under a microscope.

Phormidium under a microscope.

Algal mats at Five Mile Bay.

Algal mats at Five Mile Bay.

Waikato Regional Council water scientist, Dr Eloise Ryan.

Waikato Regional Council water scientist, Dr Eloise Ryan, examining the algal samples.