Toxic algal blooms keep lakes off-limits

By ROSALEEN MacBRAYNE

Algal blooms on Lake Rotorua and Lake Rotoiti are releasing toxins at dangerously high levels.

Concentrations of cyanotoxins - the bacteria in blue-green algae which can make people sick - have been recorded at 5000 times above World Health Organisation safety standards for drinking water in samples from the Ohau Channel.

This was a significant health risk for any water users, the Bay of Plenty and Lakes medical officer of health, Phil Shoemack, said yesterday.

Blanket health warnings for all of Lake Rotorua, adjoining Lake Rotoiti and the linking Ohau Channel have been in force for the past three months as the potentially poisonous cyanobacterial blue-green algal blooms have continued unabated.

Lakes Water Quality Society chairman Ian McLean said of the toxin confirmation: "This confirms our worst fears that the lakes are dying fast. It is a huge wake-up call to Environment Bay of Plenty and the Rotorua District Council to do something about it."

Lake Rotoiti Ratepayers and Residents Association chairwoman Sally Brock said some people who could not afford alternative supplies were still drinking lake water.

"This is third world country stuff here."

Dr Shoemack said Ohau had the highest toxicity reading so far but there was no way of knowing if it was unprecedented, because Environment Bay of Plenty had not been measuring actual toxin levels for long.

Scientists routinely did cell counts for cyanobacteria, which indicated when the buoyant blooms could become harmful.

The levels could change "overnight" and lake users should be extremely cautious.

"The presence of toxins confirms what we have always been telling people - stay away from any contact with lake water if it looks or smells off-colour." Dr Shoemack said the water should never be drunk.

"Some people believe it is fresh, it is natural, so it must be good for you. But with any lake, you don't know what has gone into the water."

Inhaling it or having significant skin contact such as swimming or showering could also be harmful.

Possible effects included diarrhoea and vomiting, rashes, hayfever or asthma attacks and, in very high doses over a long time, nervous system and liver damage.

Dr Shoemack said algal blooms on the Rotorua and Rotoiti lakes were the worst for many years but people had to be personally responsible for avoiding the dangers and not become complacent.

Lake blooms - which had the capacity to release potent toxins even after the bloom subsided - were unpredictable and largely determined by climate conditions.

A few years ago a health warning remained on Lake Rotoehu as late as August, but that lake was unaffected this year, he said.

There were no plans yet to lift the warning on Rotorua and Rotoiti, but as the weather got colder and there was less sunlight, the floating bloom masses should die off.

The possibility of more extreme levels of toxins (which are colourless and odourless) was a worry, Dr Shoemack said.

Sally Brock, who admitted to using Lake Rotoiti water for showering and domestic purposes without ill-effect, said the lakes were in a worse condition than ever.

"We have never had a health warning in force for so long or a full bloom at this time of the year. It is usually associated with summer," she said.

Association members were "fed up to the back teeth with bureaucratic inaction" and wanted a commitment from Rotorua District Council to install sewerage reticulation in lakeside settlements.

Mrs Brock said Rotoiti holiday-home owners were not coming to the lake any more and many were unable to sell their properties. "There is a lot of anger out there. How many times do you have to jump up and down?"

* A survey of the edge of Lake Rotoiti, commissioned by Environment Bay of Plenty, found more than 50 inflow pipes originally installed to supply domestic water to households.

Environmental scientist Matt Bloxham said he hoped the pipes were not still in use, despite repeated warnings of the risks of drinking or bathing in the water.

Some residents might be "unrealistically confident" that their water filters were removing toxins, when they were not, he said.

Others might still use lake water because they had done so for decades without any noticeable ill-effects.

"They underestimate the risks because they forget health impacts are often insidious. Some cyano-toxins can affect your body over time," said Mr Bloxham.

The pipe survey information was given to Rotorua District Council to track down the landowners.


Dangerous waters

* Poisonous blue-green algal blooms have returned to Lake Rotorua and Lake Rotoiti this year.

* A water sample this month was 5000 times above World Health Organisation safety standards for drinking water.

* Some Rotoiti residents are still using lake water to drink and wash in, despite repeated warnings of the health risks.