Cyanobacteria bloom suspected in lagoon

Cyanobacteria algae is shown  in this stock photo.
Cyanobacteria algae is shown in this stock photo.

A suspected sighting of potentially toxic cyanobacteria algae in the Albert Town lagoon is the first in the waterway, Otago Regional Council (ORC) resource science manager Dr Dean Olsen says.

The ORC yesterday issued a warning about the lagoon following a report of a possible sighting of the blue-green algae forwarded to the ORC by the Queenstown Lakes District Council.

A sample of the algae had been taken and results were expected to be confirmed either late today or tomorrow morning. The ORC would then modify its warning if necessary, depending on whether the algae was confirmed and if so at what levels.

Dr Olsen said it was ''pretty impossible to say'' what might have caused the algae to bloom in the lagoon, but it typically bloomed in shallow water when temperatures were high.

The lagoon is surrounded by houses and people are being advised not to use the waterway for recreational purposes. Cyanobacteria can produce toxins that are harmful to humans and animals if swallowed or through contact with skin. Dog owners are warned to be especially vigilant as the algae is particularly toxic to dogs.

Dr Olsen said an ORC warning issued last month about the possibility of cyanobacteria in the Cardrona and Manuherikia Rivers still remained.

Although rainfall last week had raised river levels, it could also loosen and shift mats of the cyanobacteria to places accessible to dogs and children.

However, a health warning issued about Lake Waihola had been lifted and the lake was now safe for public use, Dr Olsen said.

Three consecutive samples of water from the lake, taken between January 18 and 30, had confirmed cyanobacteria levels were low enough to lift the warning, he said.

However, regular ORC monitoring of Lake Waihola, the Tomahawk Lagoon and Falls Dam would continue as the cyanobacteria came and went from those waterways, Dr Olsen said.

Cyanobacteria levels in Falls Dam had never reached the threshold for a public warning, but people should still familiarise themselves with what cyanobacteria looked like and make sure their dogs and small children were safe around waterways, he said.

''We'd hate to lull people into a false sense of security by giving a clear result for somewhere when there could be toxic algae 300m upstream.

''It's just about sending out a signal to dog owners to always be aware and assume it [cyanobacteria] can always be present.''

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