Media release

Toxic algae confirmed in the Cardrona River

Friday 19 February 2016

The Otago Regional Council (ORC) has today received laboratory test results that confirm the presence of Phormidium, or toxic algae, in the Cardrona River.

The lab said that the concentration of toxins was very high, and that eating only a small amount could prove fatal to dogs.

In the past week, two dogs have died in the area after ingesting algae from the river, and ORC has erected four warning signs in the area of the poisoning.

ORC manager resource science Dean Olsen said while no other Otago waterways have tested positive for toxic algae so far this summer, he encouraged people to get in touch with the council through its Pollution Hotline (0800 800 033) if they come across the dark brown/black mats, which often contains the toxic algae.

Members of the public should not swim, fish, or carry out any other recreational activity in an affected river.

The poison can be absorbed through the skin so direct contact should be avoided.

Public Health South advises that exposure in humans may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips.

Anyone experiencing any of these symptoms should visit their doctor or local hospital immediately, including if they have had contact with dark brown/black algal mats or water in affected areas.

Dr Olsen reiterated his earlier comments that cyanobacteria can be found in any river and that monitoring the risk to dogs is extremely difficult, due to the cyanobacteria’s wide distribution, their scarcity within particular rivers, and the fact that a dog would only have to eat a relatively small quantity of toxic algal material to be poisoned.

“Although not all species of cyanobacteria are toxic, they cannot be distinguished from one another without testing. Studies have shown it is possible to have toxic and non-toxic strains of the same species within centimetres of one another”, Dr Olsen said.

Cyanobacteria mats can be identified by a strong musty odour and can vary in colour from dark brown/black when in the water, to a pale brown/white when dry. The musty odour produced by mats can be attractive to some dogs, which may eat them. The mats can also detach from the river bed and float downstream to areas where dogs are likely to encounter them.

Previous dog deaths in Otago have been linked to Phormidium, but these are the first confirmed on the Cardrona River. Given the recent rainfall in the area, mats may also be washed onto riverbanks, he said.

Pets should be taken to a vet immediately if they show signs of illness after coming into contact with algal mats or if they suddenly become ill after being around rivers or streams, especially if cyanobacteria are present.

“The most common signs that a dog might have consumed toxic algal material are lethargy, muscle tremors, fast breathing, salivation, twitching, paralysis and convulsions soon after being in or near the water,” Dr Olsen said.

For more information

For more information contact
Dean Olsen
Manager Resource Science
Otago Regional Council
03 474 0827 or 027 602 2737

Public health enquiries
Dr Derek Bell
Medical officer of health
Southern DHB
03 476 9800