Two investigations are underway following complaints over a major aerial 1080 operation near Te Anau.
The Department of Conservation (DOC) recently launched the country's largest-ever 1080 poison drop, which will cover more than 720,000 hectares of conservation land as part of the "Battle for our Birds" campaign.
Nineteen sites around the country are being targeted, with pest control work in Fiordland National Park aimed at protecting native wildlife from rats and stoats.
A DOC contractor carried out a 1080 pesticide drop in the Kepler Mountains last Tuesday and Wednesday, using helicopters based out of Te Anau Airport.
But several Te Anau residents have laid official complaints with DOC after some of the poison-laced pellets were found in publicly accessible walking tracks outside the designated area near Lake Manapouri.
Former hunter Perrin Brown says DOC's private contractor is to blame.
"On the day of the drop the helicopters were going so fast; the hoppers were going sideways," he says. "You can't tell me they don't make mistakes; that's obviously how the 1080 got in the bush."
Other complainants reported seeing helicopters taking off without having the door closed on the chopper, spilling 1080 pellets beside the loading site.
"We've found pellets washed up on the banks of the Waiau River," says Mr Brown. "That's right along the boundary. It's now the school holidays, and the fishing season is about to open. Many families are going to be there with kids right along the area of the drop zone."
He says the pellets could potentially kill a young child or household pet if eaten.
DOC's Te Anau operations manager, Greg Lind, told Mr Brown he was sceptical about the claims and has suggested the 1080 pellets were deliberately scattered around to make the department look bad.
However Mr Lind says rangers are now conducting a sweep of the area, to see how widespread the wayward pellets are. He says DOC won't be making any further comment until that investigation is complete.
Mr Brown says the poison drops are usually carried out in more remote areas, but believes it's the first time DOC has carried out such a large blanket drop in easily accessible countryside around Te Anau.
DOC is planning half a dozen more aerial operations during October, once weather conditions improve.
Environment Southland is also launching its own investigation as to whether the recent poison drop breached resource consents.