Central Interceptor

The end is in sight for the Central Interceptor project

With a planned ‘ready to commission’ timeline of mid-2026, the northern section of the tunnel can ‘go-live’ to connect up to the southern section, which commenced operation in February 2025.

The first Northern construction site to be completed was Walmsley Park in Mt Roskill. This public space has been reinstated with new planting and was handed back to Council Parks to open in December last year.


Central Interceptor's reinstatement team underway with new planting

The next three sites to be completed lie on the 2.1km Link Sewer B: Mt Albert War Memorial Reserve is about to have the carpark spaces repainted and will soon be reopened for visitors. (See image). The other two sites are Norgrove Reserve and Rawalpindi Reserve, further along Meola Creek, which are nearing the end of their reinstatement works. And Lyon Ave, on the Roy Clements Treeway north of Kerr-Taylor Park is close to completion also.

Four sites will take until mid-year to complete their work programmes and be handed to the reinstatement/replanting team (see image): Haverstock Rd in Sandringham, Western Springs, Tawariki St (on Watercare land in Grey Lynn) and Point Erin Park, Herne Bay.

Last to finish is our main tunnel site at May Road in Mt Roskill. Wastewater from Miranda Reserve in Avondale is already flowing along the new Link Sewer C to May Road and on into the southern section of the CI tunnel. After the full tunnel commissioning in mid-2026, May Road’s CI assets, particularly a new air treatment facility, will be passed to Watercare’s Operations team for on-going maintenance, along with all the new infrastructure at 17 sites across the isthmus.

Mt Albert War Memoriral lower carpark restoration

What are we building under there?

The Central Interceptor tunnel lies between 15 and 110 metres below the city surface and will run all the way from Pt Erin in Herne Bay to Māngere Wastewater Treatment Plant. With a diameter of 4.5m, the tunnel will be high enough to fit a standing giraffe inside.

Along with two smaller-link sewer tunnels also under construction, the main CI tunnel will collect wastewater from the existing network and take it to Māngere, with a controlled flow rate. The tunnel slopes at a gradient of 1:1000 so wastewater can flow downhill to Māngere.

The budget for this epic seven-year project is $1.668 billion.

Construction updates

We have 17 construction sites along the tunnel route, with some operating for three to five years, with smaller sites open for around 24-36 months.

At the bottom of the page, you can see what’s going on at each site.

The technology behind New Zealand’s largest wastewater project

To dig the main CI tunnel and lay the concrete segments behind it, we used state-of-the-art tunnel boring machines (TBMs). These gigantic machines enable us to excavate (or ‘bore’) through a wide range of ground conditions.

Infrastructure constructed by these powerful TBMs is strong and reliable and is set to last at least 100 years.

Engaging with locals

We want to update you on the construction process and hear your feedback. If you live or work near one of our sites, you’ll get a bulletin, newsletter, notice or letter, or an invitation to a public event, depending on the information we have to share.

Email us your feedback.

Supporting our wider community

Although it’s being built to last 100 years, the ambition for the project extends well beyond construction. We also want to help improve the wellbeing of communities along the tunnel route.

To support this, a cultural outcomes group is providing advice as the project progresses. This group comprises people from mana whenua, our Watercare team and contractors. Check out some of our activities.

Protecting our environment

As well as delivering significant environmental benefits such as cleaning up our waterways, we’re committed to leaving our construction sites and their surrounds in a better condition than when we arrived.