VetEnt veterinarian Erika Benton said without a postmortem she could not confirm the toxic bacteria cyanobacteria in the Clutha River was the cause of the Labrador’s death, but all symptoms led her to believe it was.
The dog owners rang the vet from the river over New Year saying their pet was "a bit wobbly".
By the time Dr Benson saw them 40 minutes later, the dog was unconscious and could not be revived.
It was the first death in her two years at the practice that she believed was caused by cyanobacteria.
There had been other deaths where vets suspected it had been the cause, she said.
People rarely saw their dog eating the algae and the alarm was usually raised when the dog collapsed or was found unconscious.
"Not everyone has such a close eye on their dog."
There was no antidote for cyanobacteria poisoning and even a small amount was fatal, Dr Benson said.
Otago Regional Council senior water quality scientist Rachel Ozanne said the council had visited the Roxburgh site on Thursday and again yesterday.
There was no sign of toxic algae then, she said.
However, the samples taken on Thursday showed low levels of phormidium, a type of cyanobacteria, so there could have been toxic algae in the area recently, Ms Ozanne said.
Dogs were at risk even from old or dried mats of toxic algae on the river bank.
"If you see brown or black mats growing on rocks in the river, or smell a strong musty odour from dried out mats of algae on the river bank be careful, keep away and let us know," she said.
Dr Benson said most people were aware of the danger of cyanobacteria and were really good at communicating "hot spots".
The danger increased the longer the dog spent in the water if toxic algae was present.
Even a little bit was ingested, was "very bad news".
• Report suspected toxic algae sightings to Otago Regional Council pollution hotline 0800 800 033
• Check if it’s safe to swim at orc.govt.nz/managing-our-environment/water/toxic-algae-sightings
- By Julie Asher
