Central Interceptor fully live, delivering a cleaner future for Auckland

Auckland is set to reap the environmental benefits of Watercare’s Central Interceptor wastewater tunnel, which is now fully operational.

The $1.66 billion project – New Zealand’s largest-ever wastewater infrastructure investment – will dramatically reduce wet weather overflows, improve the health of Auckland’s waterways and harbours, and support growth across the region for decades to come.

The Central Interceptor has already delivered significant environmental benefits. The southern half of the tunnel went live in early 2025, preventing an estimated 741,000 cubic metres of wastewater and stormwater from overflowing into the environment by 1 July this year. That’s the equivalent of almost 300 Olympic-sized swimming pools.

“The Central Interceptor provides the backbone for future projects that will further improve environmental performance, increase network resilience, and support Auckland’s growth,” says Watercare chief executive Jamie Sinclair.

The first of these projects, the Herne Bay Collector, is under way – a wastewater tunnel that will connect to the Central Interceptor when completed and contribute to further reducing wet weather overflows.

Sinclair says the completion of the 16.2-kilometre Central Interceptor tunnel is a transformative moment for Auckland.

“The Central Interceptor is a game changer for our city that will deliver lasting environmental, community and growth benefits for Aucklanders.

“This project is at the heart of our commitment to improving water quality across the region. Bringing together world-class engineering, long-term planning and strong partnerships, it delivers benefits for Aucklanders now while enabling a new generation of projects that will further reduce wastewater overflows and make a real difference to the health of the Waitematā Harbour and other waterways into the future.”

Running from Point Erin in Herne Bay to the Māngere Wastewater Treatment Plant, the 4.5-metre-diameter tunnel sits between 15 and 110 metres below ground and passes beneath the Manukau Harbour. Together with its link sewers in Mt Roskill, Blockhouse Bay and Mt Albert, it captures and transfers wastewater and stormwater flows that would otherwise contribute to wet-weather overflows.

With the northern section now in service, the full tunnel is operational and positioned to deliver even greater environmental improvements across the city.

Mayor Wayne Brown, who is also an engineer, says the completion of the project is a significant achievement that will benefit Aucklanders by reducing wet weather overflows and helping to improve the health of our harbours and local streams.

“This is Auckland’s largest wastewater infrastructure project, taking seven years to complete using a tunnel boring machine to build the gravity driven tunnel across the isthmus between Māngere in the south and the central city,” says Mayor Brown.

“Aucklanders want cleaner waterways and to be able to enjoy the likes of Browny’s pool, local beaches and marine environment.

“Delivering these outcomes while creating a smarter, more resilient network is exactly what we are committed to providing for the future of Auckland. This project shows what's possible when we invest in the right infrastructure at the right time.”

The project's successful delivery also reflects the power of collaboration between Watercare, delivery partner the Ghella Abergeldie Joint Venture, mana whenua, Auckland Council and local communities.

Construction began on the project in 2019. Despite challenges including the Covid-19 pandemic, major weather events and unprecedented inflationary pressures, the team delivered the project on schedule and close to its original budget.

“Mega projects of this scale rarely stay so close to programme and budget, particularly given the challenges faced throughout delivery,” says Sinclair.

“Working together has enabled one of New Zealand's most complex infrastructure projects to be delivered safely, efficiently and with a strong focus on environmental and community outcomes. We’re incredibly proud of what has been achieved.”

Central Interceptor facts and figures

• The Central Interceptor wastewater tunnel is 4.5 metres in diameter and 16.2km long, running from the Māngere Wastewater Treatment Plant to Point Erin in Herne Bay.
• It had 17 construction sites across Auckland.
• There are 19 shafts in total.
• Since construction began in 2019, more than 4,300 people have worked on the project.
• The tunnel has the capacity to hold 299,000 cubic metres of wastewater and stormwater.
• The giant tunnel boring machine, Hiwa-i-te-Rangi, which created the main tunnel, was named by school students after the youngest star in the Matariki cluster, which symbolises growth and prosperity. She was 190 metres long and weighed 740 tonnes.
• Hiwa-i-te-Rangi was electric, as were the locomotives used in the tunnel to remove the spoil, to replace diesel and reduce fuel use