A large-scale 1080 pest control programme across the Hunua Ranges, south-east of Auckland, has suddenly been suspended.
A conservation group opposing the drop - The Friends of Sherwood Trust - won a temporary injunction in the Environment Court, about the same time as non-toxic cereal pellets were being dropped across the ranges last week.
The trust is worried that 1080 could fall into the water supply.
Friends of Sherwood Trust lawyer Sue Grey said 1080 wouildn't break down into non-toxic products in water.
"It does break down depending on the time, depending on the temperature, depending on the dilution...it breaks down into a toxic product," she said.
"Although [Forest and Bird ] say biodegradable, it's not biodegradable in terms of safe by-products."
The non-toxic pellets used in the precursor drop are designed to entice pests like rats, possums and stoats with a taste of the bait before the toxic version is dispersed.
The drop of actual 1080 poison over the Hunua Ranges had been expected to take place by the end of this week, depending on weather
But the Environment Court ruling has put that on hold, while a full hearing is due this Thursday.
The plan is for bait to be dropped across about 23,000 hectares with about 2kg of bait applied to each hectare.
Last Thursday, three helicopters dangling large buckets darted back and forth from deep in the Hunua Ranges.
Staff from the private contracting company were wary of the two journalists permitted on the site and did not allow photography of the choppers or staff.
This was precautionary. Over the years this crew has been subject to numerous threats and abuse by opponents of 1080, which remains controversial despite the scientific and conservation communities overwhelmingly supporting its use.
"We had a pseudo-bomb that was delivered to our depot, so we had effectively a bomb-scare," said one employee.
"The bomb squad from Auckland came down and brought their little drone thing in and picked up this device and took it away. Effectively it was a hoax."
The helicopters on Thursday dropped harmless cinnamon-scented cereal pellets, which look and smell like something you might have with milk for breakfast.
The idea is that targeted pest species like rats, possums and stoats will develop a taste for food that rains from the sky.
The operation's head Rachel Kelleher, from Auckland Council, said the helicopters used two types of buckets: One which rotated and flung the bait up to 250m; the other trickle bucket was able to drop pellets precisely along drop-zone's boundaries.
She described it as like colouring in a picture.
The bait has been designed to try to be attractive only to the targeted species, including its green colour and scent.
"A lot of work is done to make sure that the bait is not attractive to birds," Ms Kelleher said.
"They are cereal pellets and our native birds don't tend to feed on cereal."
1080 sceptic won over
The first 1080 to be dropped over the Hunua Ranges was in 2015, an operation Ms Kelleher said was highly successful.
Calls of native birds like the kokako were now commonplace, she said.
But favourable weather conditions last year created an abundance of food for pest species and the birds were again under threat.
There are four reservoirs in the Hunua Ranges which supply about 60 percent of Auckland's water and the 1080 drop has some concerned about contamination.
"What we do know is that our native and threatened birds are doing extremely well under this form of pest control and in fact they need it to survive."
Ms Kelleher said the helicopters had precise GPS guidance systems and only dropped pellets a safe distance from the water. Nonetheless, the water supply would cease until rigourous testing was completed.
Local resident Mike Hepburn used to be a 1080 sceptic but changed his stance after seeing the wildlife return to the ranges.
"I'm finding there are more deer in the bush now ...and there's not as much by-kill as there used to be."
He, too, was not popular in some circles for being a supporter of 1080.
"The Facebook messages on my Facebook page can be some pretty foolish and nasty stuff."
Long-time Hunua resident and Franklin Local Board member Malcolm Bell said he also had noticed a difference in the bush since the 2015 drop.
"Nobody wants to drop a toxin anywhere but the fact is if we want the bird life and the other native life to prosper then it's the best that we've got for the moment."