Mrs Boaler said she had never seen a dog with the same symptoms in Hawke's Bay and her research pointed towards algae poisoning.
"In our opinion and the symptoms and onset and apparent relationship to something that happened on the walk do seem to fit the many aspects of the previously described cases of algae poisoning.
"But not the one that has been implicated in other rivers. There are so many different species of cyano bacteria and they all produce different toxins and different combinations of toxins and that's why it's very presumptive."
The Hawke's Bay Regional Council was notified of Billy's death and Mrs Boaler's prognosis, and signs had been erected warning users of potential dangers.
Resource Management group manager Iain Maxwell said the council was investigating the death, increasing testing regimes and warning the public to be wary around waterways. A council spokeswoman said no other cases had been reported in the region.
"We are still waiting for the final test results to come back relating to the dog death," she said.
"We have had no other reported cases elsewhere in Hawke's Bay this summer, however the lab testing the sample did mention there have been other cases reported to them from around the country."
It was too soon to say if other cases were from the same algae type as that implicated in Billy's death.