Dog-owners will be discouraged from taking their pets into Auckland's Hunua Ranges for at least four months after a major drop of 1080 poison began today.

Watercare has taken two of its four Hunua supply dams out of service until they receive a clean bill of health, and three regional parks have been closed to the public for five days.

That follows what Auckland Council says was the successful completion of a 1080 bait drop by three helicopters in the first of two large blocks of forestry covering 21,500 hectares.

The council expects to give the second block - which includes the other two supply dams - the same treatment in seven to 10 days, weather permitting.

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But although it is confident heavy rain will break the 1080 sufficiently to reconnect the first dams within the next week, it acknowledges the poison will remain in the carcasses of dead pest for far longer.

Hunua resident Angela Lloyd fears she will have to keep the only working dog she uses to round up her small cattle herd tied up for up to two years, and is also concerned for the health of her seven event and dressage horses.

"The toxin can last in carcasses for two years, and because we're on a river, we get a lot coming down the waterway," she said.

"Dogs have died after two years and a lot have died eight to 12 months after."

A locked gate and sign in the Hunua Ranges Regional Park yesterday. Photo / Supplied
A locked gate and sign in the Hunua Ranges Regional Park yesterday. Photo / Supplied

Council operations leader Rachel Kelleher acknowledged a need for people to keep their dogs out of the dosed area for at least four months, and possibly for up to double that time, but was confident monitoring would allow the all-clear to be given well within that period.

"We'll be doing real-time monitoring of carcass breakdown, which will give us a much more accurate picture of how quickly the risk to dogs disappears."

The council had meanwhile issued vomit-inducing medication and muzzles to dog-owners on request.

She said Ms Lloyd's horses would be safe as the council had directed the helicopters to stay 80 metres clear of her land, although she added that it was good practice for dog-owners to discourage their pets from feeding on dead pests at all times, given the use of poisons by many private property owners.

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Although no-flying and poison exclusion zones have also been designated around the reservoirs, Ms Lloyd she had seen a flight path which went over a stream near her property.

"And we saw today that they're pretty loose with their helicopter flying," she added.
Ms Kelleher said today's operation had been monitored by an Auckland Regional Public Health Service auditor "and all the exclusions for the reservoirs have been met."

The auditor, based at the poisoned bait loading site, had access to computerised flight data downloaded from the helicopters throughout the day.

Logging contractor Mark Nyhoff said he and his nine employers working in a private pine forestry block adjoining Hunua parkland were concerned to see helicopters "encircling us", although he did not know whether they were carrying pellets laced with 1080 or pre-cursor non-toxic cereal designed to get rats, stoats and possums used to taking the bait.

"They were going to go right through our job, and we said that ain't going to happen, and now they are going around us."

Mr Nyhoff said it wasn't until about noon that he was shown a map of the intended drop zone.

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He said he had been working in areas treated with 1080 for more than 30 years and did not accept that it had only a limited impact on the bird-life it was supposed to be helping.

"We see all the side effects of it - if you go into the Kaingaroa Forest (near Taupo), you don't hear any birds at all - that place is just silent."

Ms Kelleher said the council had written approval from owners of more than 2000ha of private land to include them in the pest control operation, and had specifically excluded the area being logged by Mr Nyhoff's team.

The council says pests are having a devastating impact on native birds - including kokako - and fauna in the Hunuas.

It says no fledglings of six monitored pairs of kokako have survived from the 2014-15 breeding season.