Lake algae blooms continue to be low

The low counts of cyanobacteria (blue-green algae) in the Rotorua lakes have continued throughout January, according to the latest Environment Bay of Plenty monitoring.

All lakes in the region remain safe for swimming, with the exception of Lake Rotoehu’s Otautu Bay where a health warning remains in place. Cyanobacteria activity in the main body of Lake Rotoehu remains relatively low and is currently safe for swimming.

Environment Bay of Plenty Environmental Scientist Matt Bloxham said February, March and April are historically the most problematic months for algae blooms.

“Every season tends to be different so anything could happen between now and June but hopefully we may be spared significant bloom activity for the remainder of summer.”

Environment Bay of Plenty Group Manager Water Management Eddie Grogan said it had been encouraging that Lake Okaro, where there have traditionally been significant blooms in recent years and subsequent health warnings in place, had had very low counts for cyanobacteria in November, December and January.

Data suggests that if Lake Okaro was going to bloom it would have by now.

“Environment Bay of Plenty has been working with people in the Lake Okaro catchment to help reduce the nutrients in the lake, including sediment capping, which prevents nutrients held in the lakebed from being released into the water column; creation of wetlands; and support for environmental programmes. This combined activity will have had a positive impact on the low bacteria counts for Lake Okaro this summer,” Mr Grogan said.

Environment Bay of Plenty would continue to regularly monitor the cyanobacteria (blue-green algae) levels in the Rotorua lakes.

Cyanobacteria are capable of producing toxins that are harmful to humans and animals if swallowed or if exposed to skin, such as may occur when swimming, skiing or kayaking. Cyanobacteria bloom as a result of a combination of excess nutrients in the lakes and climatic and biological factors.

Rivers in the region also appear to have lower levels of the cyanobacteria Phormidium than in previous years and a health warning on the upper Rangitaiki River was lifted earlier this month. Phormidium, a mat forming cyanobacteria that attaches to the river bed, can produce a powerful neuro-toxin, which if accidentally ingested can be harmful to humans and animals.

Mr Bloxham said the low percentage cover of phormidum in the region’s rivers presently is mainly due to recent heavy rain and scouring. “A lack of rain and low flows could easily see the return of extensive mat development so the public needs to remain vigilant.”

People are encouraged to look on Environment Bay of Plenty’s website for the latest water quality monitoring and lake health warnings: www.envbop.govt.nz keywords lake health warnings. Residents and visitors are also advised to look out for warning signs and check the latest Toi Te Ora – Public Health advisories on www.toiteorapublichealth.govt.nz.

ENDS

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