‘Spectacular’ lake foam is considered safe
For immediate release: 18 June, 2010

It may look as though Lake Rotorua is turning into a nicely foamed latte near the Ohau Channel – but the foam on the shore may be produced by an algae species that proliferates in winter.

Environment Bay of Plenty environmental scientist Matt Bloxham says the foam that has been showing up along the lake shore over the past few months, and that has been quite conspicuous over the past day or two, is fairly consistent with foam-producing algae.

“Every so often we get high numbers of Kirchneriella, a foam-producing algae. It was first identified as a ‘new’ species to the Rotorua lakes in 1998 and since then has occurred fairly sporadically The foam it produces can be quite spectacular at times.”

He said because the algae reduces the surface tension of the water, foam production becomes more likely, particularly where there is substantial mixing and aeration of the water, such as occurs in the Ohau Channel and in the Kaituna River below the Okere Falls.

“Different species of algae proliferate at different times and this one typically has a higher biomass in winter. What is slightly frustrating is that by the foam appears, numbers of the offending algae species may have ebbed and we are presently seeing only low numbers of Kirchneriella in our samples.”

“There is more than one freshwater algae species that can potentially produce foam, so the possibility remains that the foam may have been caused by another species. Environment Bay of Plenty will take further samples in the coming weeks to resolve which species are responsible,” he said.

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