A trust opposing Auckland Council's 1080 poison drop in the Hunua Ranges has won a court injunction temporarily suspending the operation.
The council had already begun covering the bush with non-toxic pre-drop pellets, to be followed up with 1080 within seven to 10 days, despite being aware of the application to the Court from the Friends of Sherwood Trust.
Judge Jeff Smith said the pre-feed drop had commenced just prior to a telephone conference.
"The Council proceeded with the drop in the knowledge of this application and therefore at its own peril in the event that the interim orders are granted for the long term."
The aerial poison operation was publicly notified at the end of August.
The purpose was to reduce pest numbers and maintain the natural habitat of the Hunua Ranges. Pest levels had risen again after a successful 2015 operation.
Sodium fluoroactetate (1080) was to be applied by helicopter to 30,501ha across the Hunua Ranges, an area that provides about 65 per cent of Auckland's drinking water and houses four large water reservoirs.
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.
Despite these measures the trust, represented by lawyer Sue Grey, raised concerns 1080 would fall into the water supply.
The trust had applied for orders preventing the deposit of any 1080 poison baits in the bed of any river in the Hunua Water Catchment.
The trust was also concerned about the potential the impact of 1080 on the flora, fauna and water supply.
Judge Smith granted an interim order preventing the council from conducting an aerial drop of 1080 in the area before 4pm, Thursday, September 13.
A hearing into the issues would commence at 10am on Thursday, September 13.