A farmhand did not face animal cruelty charges because a council wrongly said drowning possums was a humane way to kill them.
SPCA staff were investigating the actions of a Waikato man after receiving information he had deliberately drowned a possum in a water trough at a rural property.
He admitted he had repeated the act up to five times previously because he had read it was a humane method of killing the pests.
Under the Animal Welfare Act, anyone who wilfully ill-treats an animal causing its death can be jailed for up to five years or fined $100,000.
But the man pointed the SPCA to the website of the Greater Wellington Regional Council (GWRC), which advised anyone who had live trapped possums to shoot them, drown them or take them to a vet to be euthanised.
Because of the misinformation, any prosecution was doomed to fail and the SPCA had to resort to formally warning the farmhand.
GWRC biosecurity manager Davor Bejakovich said the website advice had come from a brochure produced in 2003 that contained "best-practice information at the time".
"The information was removed and all the hard copies of the brochure destroyed when SPCA contacted council in March and pointed out that brochure contained erroneous information," he said.