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Health Warning: Potentially toxic algae in Waikaia River

Media Release

Health Warning: Potentially toxic algae in Waikaia River

Monitoring carried out by Environment Southland shows a high abundance of the naturally occurring and potentially toxic benthic cyanobacteria (blue/green or brown/black algae) in the Waikaia River in northern Southland.

Cyanobacteria algal mats have been observed floating downstream, which means the algal could also be present in the Mataura River, but this is yet to be confirmed.

People and animals (dogs are particularly susceptible) should avoid contact with the Waikaia River from Piano Flat downstream, including the main stem of the Mataura River until health warnings are removed.

Cyanobacteria can produce toxins that are harmful if swallowed or if they come into contact with skin. Exposure may cause skin rashes, nausea, stomach upsets, and tingling and numbness around the mouth or fingertips. If you experience symptoms after contact with contaminated water, contact Public Health South and see a doctor immediately. Boiling contaminated water does not remove the toxins and drinking it is not recommended. Animals that consume cyanobacteria should be taken to a vet immediately.

Cyanobacteria occur naturally and can increase rapidly during warmer periods. Cyanobacteria usually grow as dark brown/black mats attached to rocks in the river or accumulate on the surface in shallow, slow-flowing areas. They often have a strong, musty smell.

“All Southlanders should be vigilant as cyanobacteria could be growing in other rivers that aren’t monitored on a regular basis. If anyone does come across cyanobacteria they should avoid contact, stay out of the river, and report their observations to Environment Southland. Photographs are an ideal way to do so,” say Environment Southland surface water quality scientist Roger Hodson.

Cyanobacteria concentrations can vary quickly with changing environmental conditions; for example, high river levels will remove cyanobacteria.

Environment Southland is continuing to monitor the situation in the Waikaia and Mataura Rivers and Public Health South will advise when the health warning is lifted.


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