A legal bid to prevent Auckland Council dropping 1080 poison in the Hunua Ranges has failed.

The council had advised the public of the planned aerial poison operation at the end of August.

The Friends of Sherwood Trust went to the Environment Court earlier this month and won a court injunction temporarily suspending the operation.

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 planned the 1080 drop 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.