Despite Lake Waikare's multi-coloured hues, the algae rampant in the lake is not toxic, says Waikato Regional Council.
A naturally occurring algae known as monoraphidium in the north Waikato lake has caused the lake to bloom red, pink and copper since early this year.
"This algae is used in the food industry for food colouring. I have no reason to believe it's toxic," said Waikato Regional Council water scientist Bill Vant, when he appeared on TV3's Campbell Live last night.
The mystery remains as to why the particular algae's numbers were almost 300 times higher than this time last year.
Long-time Ohinewai farmer Malcolm Lumsden suspected the culprit was the two latest dry spells.
"I think that it's an event and it's probably caused by the two very hot summers and very little rain so we haven't had the flushing that we would perhaps normally get."
Despite the rest of the country having recovered from the latest thirsty spell, Lumsden said "it's still dry here".
Vant said council first received reports on the lake's red colouring early this year.
"It hasn't been till May that scientists at the Cawthron Institute and University of Waikato have been able to confirm the culprit is likely to be the higher densities of monoraphidium this year.
Council said multiple human pressures, such as farming and water abstraction that began in the 1940s, have degraded the water quality of Lake Waikare and the wider lake catchment.
However Lumsden refuted this, and said the numbers of farmers in the area hasn't changed a lot since the 1960s.
"The easiest thing to do is to throw it in the farmers' face and say it's all the farmers' fault, but it's not."
He said Waikare was an ash pit, left over from Taupo eruptions, and geothermal vents were active along its eastern foreshore.
A project involving the council and river iwi partners will set targets and limits for water quality in the Waikato and Waipa river catchments.
Conservation partnerships director for Department of Conservation Nicki Douglas said DoC is keen to find a long-term solution.
"The Waikato Regional Council is the lead agency in managing the lake and we're working with them on this issue."
It is unclear how long the discolouration will continue.
- Waikato Times