A new survey has found that sediment levels in the Porirua Harbour have more than doubled in the last five years, despite a decade of efforts to clean it up.
It's the product of cutting down trees, building houses, farming and the construction of the Transmission Gully motorway in Wellington. It's putting the health of local wildlife at risk and leaving locals frustrated.
But NZTA predicts it will have offset the damage it's caused in seven years, with erosion measures in place.
Greater Wellington Regional Council environmental scientist Megan Oliver told 1 NEWS that "compliance is certainly one of those areas that we're going to have to be working more in".
Ngāti Toa chairman Taku Parai says he's disappointed by the results of the latest survey.
"They've said a lot of things over the years, reports say different and I guess for the iwi we need a bit of action in terms of tidying this harbour up, making it a place for the community to come and feel safe."
The survey of the estuary floor shows the depth of run off is increasing around four millimetres each year, compared to a healthy limit of one millimetre.
Ms Oliver says, "If you're a rig shark and you're a hunter and you need clear water to find your prey than obviously fine muds suspended in the water column impede your ability."
Naomi Solomon from Ngāti Toa says, "I know that we can't get the harbour back to what it was anytime soon but it's our hope that it will be restored and people can interact with the harbour in the ways we have."