Greater Wellington Regional Council is spending a decade building a fence to protect thousands of hectares of native forest from pests.
RNZ was given a look at the area of Wainuiomata Regional Park which was normally roped off to the public due to its proximity to the capital's water source.
Driving through the native bush, rātā trees estimated to be hundreds of years old were in full bloom - offering spots of bright red amongst shades of light and dark green.
But underneath the tree canopy was a problem that had been brewing for years.
Photo: RNZ / Mark Papalii
The forest floor's undergrowth had been largely cleared of almost everything besides plants that tasted bad to pests or were difficult to eat for pigs, goats and deer.
The regional council's delivery director Jack Mace told RNZ that prevented future plants and trees from being able to grow after older ones died.
"We are controlling possums in here and we are now increasingly controlling deer, pigs and goats."
Mace said there was a "constant wave" of pests coming in from lands near the water catchment.
"So, what we are looking to do is to build a deer, pig and goat-proof fence around the whole valley so we can effectively eradicate them around that whole area."
Photo: RNZ / Mark Papalii
The fence was set to cost $5.9 million over a 10-year period and would protect 7400 hectares of forest.
He said it was not a Zealandia-style fence but more a fence built specifically for larger pests.
"Our fence that we'll build won't be sufficient to keep predators like stoats and cats out."
Mace noted there was a business case to fence off part of the area which would protect it from all pests but that would need central government funding.
Photo: RNZ / Mark Papalii
The forest has been home to the North Island brown kiwi for 20 years ago, a population that had been increasing due to predator controls.
He said the richness of the forest was incredible.
"Hundreds and hundreds of species down here. What's special about this area is that we have got six or seven different forest types."
Recently workers in the forest had found critically endangered species such as New Zealand's only indigenous fully parasitic flowering plant Dactylanthus and short-tailed bats.
"Even where we have been in here for over a hundred years, we are still finding things."
The project is due to be completed by 2034.
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