ORC manager resource science Dean Olsen said the dog’s symptoms and its contact with water and algal material before the onset of symptoms, suggested that cyanobacteria poisoning was likely. Follow-up surveys of the river by ORC found cyanobacteria mats present in the river in the area the dog was playing.

“This sad incident, which is clearly distressing for the dog owners, highlights the risks posed by toxic algae to dogs,” Dr Olsen said.

“The growth of cyanobacteria, which form dark brown to black mats growing on the bed of the river, is common during periods of low river flow and warm temperatures,” 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/whiteish colour 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.

Cyanobacteria such as Phormidium occur naturally throughout New Zealand. In high river flows they are flushed away, but lower flows prevent this flushing effect and warm weather promotes their growth, meaning blooms can develop quite quickly.

Previous dog deaths in Otago have been linked to Phormidium, but not in the Cardrona River. Given the recent rainfall in the area, mats may also be washed onto riverbanks.

They can be found in any river. Monitoring the risk to dogs is extremely difficult, due to their wide distribution, scarcity within particular rivers, and the fact that a dog would only have to consume a relatively small quantity of toxic algal material to be poisoned.

Although not all species of cyanobacteria are toxic, they are unable to 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.

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.

Members of the public should report any possible sightings of toxic algae to the ORC pollution hotline on 0800 800 033

ENDS
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