Work is underway to repair a broken sewage pipe in Eastbourne.
The main wastewater outfall pipeline next to the pump station in Days Bay burst on Saturday afternoon.
The pipe has leaked treated and untreated wastewater into the harbour.
The overflow has also forced the closure of three public beaches, at Days Bay, York Bay and Sunshine Bay.
Wellington Water head of network management Jeremy McKibbin said crews had drained much of the main outfall pipe and a pump was being installed to ensure it was totally drained.
The final draining was expected to take a few hours.
McKibbin said traffic management was in place, with part of Marine Drive around Sunshine Bay down to one lane until the repair works were completed.
The repair was "complex" and likely to take several days, with multiple pump stations and pipes that were supplying flow to the leak site.
"In order to repair the leak, we've had to shut down three pump stations and divert flow from the Seaview Wastewater Treatment Plant to the Waiwhetu Stream."
McKibbin said they were taking the situation seriously and were doing what they could to minimise the impacts to the environment and the community.
In the meantime Eastbourne residents are being asked to flush toilets less and avoid taking long showers to conserve water.
McKibbin said people were also advised against swimming in the water or collecting seafood.
Wellington Water said it would continue sampling the affected areas and tankers would remain in place to transport wastewater to the Seaview Treatment Plant for treatment until the repair was completed.
Meanwhile, local penguin expert Mike Rumble told RNZ the local penguin haven had been checked over the weekend and they have not been affected by the pollution.
Taranaki Whānui chief executive Kara Puketapu-Dentice said mana whenua were "deeply concerned and disappointed" by the damage caused by the wastewater overflow.
"This is the latest event in what has been a recurring issue of both treated and untreated wastewater into our precious coastal and marine environment.
"The leaders of Te Atiawa Taranaki Whānui ki Te Upoko o Te Ika have agreed to place a rāhui covering Waiwhetū stream, the eastern portion of Te Whanganui-a-Tara to Parangarehu (Pencarrow Point) and Te Awa Kairangi (to Waione Street Bridge) for as long as the discharge continues."