Rotorua lakes watched more closely for algae

Published: Fri 10 Dec 2004 11:44 AM
Friday 10 December 2004
Rotorua lakes watched more closely for algae
Rotorua’s lakes are now being watched more closely for the onset of algal blooms.
Environment Bay of Plenty has stepped up its schedule for checking blue green algae levels in four lakes that hosted potentially harmful blooms last summer – and are likely to do the same again this year.
Since November, Lake Rotorua, Lake Rotoiti, Lake Rotoehu and Lake Okaro have been undergoing weekly, rather than monthly, sampling at nearly 20 different locations. Other lakes will be monitored if they show signs of deterioration.
Environmental scientist Matt Bloxham says the more intense monitoring will continue until blooms subside, probably around next winter.
Mr Bloxham says, for the first time, samples will be taken from the middle of two lakes instead of just at the lake edge. He hopes this will help gauge the gradual build-up of algae in Lake Rotorua and Lake Rotoiti and provide a “primary warning device” for the likelihood of blooms. It should give more consistent results, he says, because mid-lake samples are less affected by wind concentrated blooms, which can collect at the edge of a lake. Mid-lake samples also provide deeper cross-sections, with 15m tubes used for the task.
Blue-green algae are microscopic plants that occur naturally in most waterbodies. However, algae can multiply rapidly when the water has too many nutrients, like nitrogen and phosphorus. Under calm conditions, they can then form into surface blooms, which are sometimes toxic.
When Environment Bay of Plenty testing shows water has too many blue-green algae, the Medical Officer of Health will issue an official health warning advising people not to swim or come into contact with the water.
Mr Bloxham says conditions are becoming more favourable for blue-green algae activity and health warnings may need to be put in place soon. He urges people to keep checking the warning status for the lakes by visiting Environment Bay of Plenty’s blue-green algae health warning web map ( or by calling Environment Bay of Plenty on 0800 ENV BOP (368 267) any time.
Health warnings are also publicised over the radio and with signs at the lake edge of affected bays. However, algal blooms can form over a matter of hours, so there are not always warning signs in place, Mr Bloxham points out. “So people need to assess the situation before entering the water even if there are no warnings in place.”
If the water looks milky green, has a surface layer, or has globules floating in it, “play it safe and go elsewhere”.

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