Algal bloom no risk to improving lake health

For immediate release: 22 November 2010

An algal bloom on Rotorua’s Lake Ōkaro which led to a health warning late last week does not mean the lake is deteriorating again, according to Bay of Plenty Regional Council.

A health warning was issued for Lake Ōkaro on Friday as routine summer monitoring results from the Regional Council confirmed blue-green algal blooms, which are potentially toxic. Medical Officer of Health Dr Neil de Wet said blue-green algae were present at levels that may result in adverse health effects so it was advisable for people to avoid contact with the water.

Lake Ōkaro, about 20 km south of Rotorua, near Rainbow Mountain is prone to blooms, particularly in November, and some can persist for several months. The previous week the Regional Council had celebrated a reduction in the Trophic Level Index or TLI ¬(a number used to indicate lake health, where higher numbers indicate worse water quality) for Lake Ōkaro from 5.3 in 2008/09 to 4.7 for 2009/10.

Group Manager Water Management Eddie Grogan said while the Council was excited about the reduction in TLI, nature had issued a reminder that lakes were dynamic biological systems.
“The species of bloom is Anabaena spiroides, which are capable of producing a toxin, so a precautionary approach has been taken. At a TLI of 4.7 there is still a significant amount of nutrients (nitrogen and phosphorus) present in the lake waters and blooms will still occur, just as they do in other nutrient rich lakes.
The bloom did not mean that the TLI value had reversed, as TLIs were calculated over a whole year, he said.
Signage has been erected advising lake users of the bloom, and weekly monitoring of the main lakes and rivers in the Bay of Plenty will continue throughout the summer.

Health authorities advise that contact with toxins from algal blooms can trigger asthma and hayfever attacks in susceptible people, as well as causing skin rashes, stomach upsets and in some cases neurological effects such as tingling around the mouth, headaches, breathing difficulties and visual problems.

If the water has a musty smell, appeared murky with a blue or greenish tinge, or if there is a scum on the surface, people should avoid contact and pets should also be kept away.

ENDS

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