But in a judgment issued today the court said: "We are not persuaded that there is likely to be serious harm to the environment if the proposed application proceeds.
"On balance, for the reasons expressed above we consider that the overall justice of the case favours the interim order not being continued."
Auckland Council and the Department of Conservation planned the 1080 drop to reduce pest numbers and maintain the natural habitat of the Hunua Ranges in an area known as Kohukohunui. Pest levels had risen again after a successful 2015 operation.
Sodium fluoroacetate (1080) was to be applied by helicopter to 30,501ha across the ranges, an area that provides about 65 per cent of Auckland's drinking water from four large water reservoirs.
The Auckland Regional Public Health Service had developed safety measures for the drop, including a no fly zone designation, buffers of 20-50m around water reservoirs and exclusion buffers of 200m around any water intakes.
The reservoirs were also to be disconnected from the water treatment plant while bait was being laid and before it became degraded. They would only be reconnected when water quality tests showed no detectable level of 1080.
The water treatment plant at Ardmore is expected to remove any particle residues from the 1080 bait and carcasses of dead animals, should any find their way into the reservoirs, according to the court decision.
Environment Judge Melanie Harland, assisted by two Environment Commissioners, said the information provided by the council about the regulation, planning, delivery and monitoring of the proposed aerial drop of cereal baits laced with 1080 was comprehensive.
"The detail provided is sufficient to show that the discharge of the 1080 pellets is necessary, will not be indiscriminate, and has been carefully planned.
"It will be governed by the conditions applied to the permission by the Public Health Service to address this particular operation."
"The documents provided by the council make it very clear there are risks to the use of 1080. We consider the methods proposed to manage those risks are appropriate and adopt the necessary precautions."
Harland said there were difficulties with the admissibility of most of the evidence filed by the applicants regarding potentially adverse effects of the poison drop because it was opinion rather than expert evidence. On some matters there was too little information about the context of the alleged bad effects or historical events.
An organic farmer, hunter and neighbouring land owner expressed concern to the court that carcasses of poisoned animals would be concentrated in water courses that drain into his property, and that this could affect his water supply and pets.
He believed animals poisoned by 1080 were drawn to water, but this was found not to be the case in research cited by a DoC witness.
The applicant's witnesses stated that at least four dogs died of suspected 1080 poisoning during or after a 2015 operation in the area with 1080. The council, however, said it was aware of only one death, the pet named Lulu, and one other suspected case.
The judge said the council had tried to manage the danger to dogs by giving out muzzles, emetics and precautionary information to owners and occupiers of nearby properties.
The council's Mace Ward said, in a statement, after the verdict was released: "The court is satisfied that an extensive consultation programme has been undertaken by the council and DoC to engage with those people who have the potential to be adversely affected by the proposed operation."
"This operation is vital to protect biodiversity in Kohukohunui, home to a range of threatened bird and plant species, including the only naturally occurring population of endangered native kōkako."
