The poison 1080 has been found in the stomach of a pet dog which died at a home near Auckland Council's massive park possum control operation.
The dog's owner, Penelope Young, who lives in the Hunua Ranges, 45km southeast of the city, said toxicology lab tests were done on the stomach contents of her five-year-old retriever, Lulu, who died on September 23.
Gribbles Veterinary had confirmed the test result supported a diagnosis of 1080 poisoning.
On September 22, the council reopened parkland in the ranges to the public after finishing aerial drops of 1080 bait over 17,000ha.
Penelope Young said her property at the bottom of the ranges was a "supposed safe area", outside the drop zone and buffer zone and all necessary precautions were taken.
"Lulu died three weeks after they dropped the poison and we were told it was okay but keep an eye on your dog, which we did.
"But they neglected to tell us that a poisoned possum carcass would wash down the Wairoa River alongside our property and Lulu has taken a chew and a swallow.
"If three weeks after the drop you can't walk your dog on your own property, there is something seriously wrong with that poison."
Penelope Young said her "healthy little dog" had been kept inside at nights but on September 23 was banging into things, shaking and frothing.
She broke from her chain and ran off into the night only to be found dead in a water hole.
She said she was taking the pathologist's report to the police station to support her legal action against the council.
"It's a crime against a dog on its own property."
SPCA Auckland chief executive Andrea Midgen said it was opposed to the use of 1080 and urged the Government to seek more humane alternatives for pest control.
"Maybe they have to look past its being cheaper and look at the greater good."
Auckland Council biodiversity manager Rachel Kelleher said the council had offered to contribute to the toxicology test and to provide a muzzle and an emetic for the family's jack russell terrier, Poppy.
"Council has taken extensive steps to inform the public, visitors to the park and, in particular dog owners adjacent to the operational area, of the safety precautions they should follow in an area treated with 1080.
"However, the loss of a family pet is deeply upsetting and our thoughts are with the family," said Ms Kelleher.
The council understood the lab report said that the cause of Lulu's death was exposure to 1080 but no one had observed the dog scavenging a poisoned possum.
Ms Kelleher said people must vigilant in supervising their pets and not allowing them to scavenge, because the drop zone would remain hazardous for dogs for at least four months and possibly more.
In 2011, Parliamentary Commissioner for the Environment Dr Jan Wright warned in a report that without the use of 1080, many native plant and animal species would be lost.
Her report urged greater use of the poison.