Algae’s presence prompts river warning

Potentially toxic algae phormidium has been found in the Waianakarua River. PHOTO: SUPPLIED/ORC
Potentially toxic algae phormidium has been found in the Waianakarua River. PHOTO: SUPPLIED/ORC
The Otago Regional Council has issued a warning after potentially toxic algae phormidium was found in the Waianakarua River this week.

A member of the public reported a sighting of phormidium near the Riverside Haven Holiday Park, and samples collected by the council confirmed its presence.

Council freshwater scientist Hugo Borges said phormidium could be fatal to dogs, which were often drawn to the musty smell of washed-up algal mats, and humans, if they ingested any pieces of it while swimming. Dogs should be kept on a leash near the river and people should keep clear of the water.

Mr Borges encouraged people who lived in the Waianakarua area or regularly visited the river to become familiar with phormidium so they could easily identify it.

The algae was naturally occurring and more common in summer when low rainfall, warm temperatures, the right level of nutrients and more sunlight created an environment in which it could thrive.

In perfect conditions, it could grow ‘‘exponentially’’, and once it was well-established in an area, it was ‘‘very, very difficult’’ to get rid of.

It was becoming a ‘‘big problem’’ across the country, and the only solution was to improve water quality, Mr Borges said.

The council monitored popular swimming spots across the region and regularly updated water quality data to the Land Air Water Aotearoa (Lawa) website, advising people of any areas unsuitable for swimming, or where caution was advised, but it also relied on reports from the public.

More information on potentially toxic algae, and sightings, is available on the ORC website.

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