The Department of Conservation is angry the actions of a contractor has painted its pest-control operations on Stewart Island in a bad light.

A former employee for a Doc-contracted pest controller lifted the lid on a 1080-poison dumping case this week, in report by Newshub.

He claimed as much as 75kg of the poison was buried in the island's national park.

Isaac, who did not want to reveal his surname, said staff were meant to put the 1080 in bait bags then staple the bags up in trees but instead he was instructed to bury them in the ground.

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"Sadly I was involved in this job. People will want to know what actually happened," he told said.

"If an animal had eaten it, it would have died a cruel and painful death, the way 1080 kills."

Newshub also reported a second dump had been discovered.

The contractor, who Isaac alleged had instructed the first dumping, was named by Newshub as Southland-based pest controller Tony Leith.

Doc acting deputy director general for operations Reg Kemper said a contractor had confirmed three bags of possum cereal bait, "containing a small amount of 1080", were left in the remote back country during a five-month ground-baiting operation.

"He has assured us that it is a one-off incident."

Leith did not respond to the Otago Daily Times when an attempt was made to contact him yesterday.

Isaac said he went to the media after a photo of a dead kiwi surfaced on social media.

Many had suggested 1080 poison was the cause of the kiwi death.

Kemper said the photo was taken 10km from the supposed dumping site, and it was extremely unlikely the kiwi death was associated with 1080.

However, he was disappointed Doc's pest-control work on Stewart Island had been been undermined by the actions of an individual contractor.

"Only this week, the department met with the pest control industry reps to reinforce Doc's focus on safety and quality in all pest-control operations."

National Party conservation spokeswoman Sarah Dowie has called for an urgent investigation.

"It is a horrible breach of the trust we place in the workers responsible for helping to protect our native species."

Kemper said the incident had been reported to the Environmental Protection Authority, police, Environment Southland and the Medical Officer of Health.

Doc was also investigating.

Stewart Island-based Southland district councillor Bruce Ford acknowledged there would be a lot of scrambling from various parties as they dealt with the fallout.

He said dumping large amounts in one place was not a good look but he felt the kiwi population on Stewart Island was thriving at the moment.

Ford said many in the township got wind of the story brewing when a camera crew was spotted on the island this week.

- Logan Savory