New Zealand is "lucky" to have 1080 in the battle against predatory species, says former Parliamentary Commissioner for the Environment Jan Wright.
Without it, we'd "lose the battle" and with it, many of our native species, she told The AM Show on Thursday.
"The Department of Conservation isn't doing this because it's fun - they're doing it because it's absolutely serious. There's no gain for them in this - it just makes them very unpopular."
Anti-1080 protesters toughened their stance in recent months, and this week the Environment Court put a temporary injunction against a planned drop of the poison in Auckland's Hunua Ranges, which supplies nearly two-thirds of the city's drinking water.
"We are playing an experiment on the people of New Zealand while we are putting this poison that's known to have possible fertility and cumulative effects into New Zealand water supplies," said lawyer Sue Grey.
When Dr Wright was tasked with evaluating the effectiveness and dangers of 1080 in her old job she went in with an open mind, admittedly not knowing a lot about the poison.
"A result of extensive investigation, following all the evidence, looking at all the research that's been done over the years, I concluded we were very lucky to have it."
No tests done on drinking water supplies have ever shown a risk from 1080, she says.
"After 1080 drops within the next 24 hours there have been samples taken, and it's been detected in very, very, very few of them, at levels far too low to affect human health."
She suspects the Environment Court's decision had more to do with points of law, than concern over the environment impacts. Auckland Council says similar arguments against 1080's use have previously been dismissed by the High Court.
"The arguments raised in the application have been refused by the High Court in previous proceedings brought by the same applicant," it said in a statement.
Dr Wright says 1080 is a deadly poison, but it's used in concentrations about 30 times less than it was 50 years ago, and there's nothing that comes close to being as effective.
"We are engaged in a battle for the survival of our native species here. It's worth pointing out Forest & Bird are fully behind it, people who know this stuff are behind it. Admittedly people are concerned - you're dropping poison out of the sky, it makes you uncomfortable. This is not a good thing to be doing, but we don't have a choice."
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Dr Wright says DoC wants to phase out 1080 as newer, more precise systems for controlling predators are developed, but 1080 "absolutely vital" in the meantime.
"We'd lose the battle early on if we don't keep using it."
Dr Wright's comprehensive report is available online. She'd like 1080 opponents to read it before continuing their crusade.
"Calm down. Go to the website, look at the report that I wrote, then look at all the evidence that we cited. Look at it, think about it, and think about what the alternatives are.
"It was very seldom in my job for 10 years that I came out with such a strong conclusion - I was blown away by how good it was, considering the opposition to it. And in my job, as politically independent - not getting any financial gain from this - I just said it straight, and I continue to say it straight."
A decision from the Environment Court on whether Friday's planned drop will go ahead is expected on Thursday.