Northern Suburbs Ocean Outfall Sewer (NSOOS)

Construction of the NSOOS in the late 1920s

Courtesy: Sydney Water / Water NSW Historical Research Archive – 30.5.29-3

We own and operate 26,169 kilometres of wastewater pipes across a network that services over 5 million customers across Sydney, the Illawarra and the Blue Mountains.

The Northern Suburbs Ocean Outfall Sewer, commonly known as the NSOOS, is an important part of our wastewater network. This vital piece of infrastructure runs along the north side of the Parramatta River, extending as far west as Blacktown and transporting wastewater all the way to the North Head Water Resource Recovery Facility in Manly.

The NSOOS was built progressively between 1916 and 1933 and was mostly tunnelled through rock, deep underground. It was the third major wastewater system built to service a rapidly growing Sydney and was significant in the development of the north shore, inner and north western suburbs of Sydney.

Thanks to its impressive scale – around 3.5 metres high by 2.6 metres wide – the NSOOS delivers wastewater services to 1.7 million people across Sydney’s Western and Northern suburbs. In fact, the 28km-long NSOOS collects around 25% of Sydney’s total sewage each day.

We're making our wastewater network more reliable

When it was built, concrete was used to line the NSOOS and protect the rock from corrosion caused by wastewater. Over time, this concrete has deteriorated, resulting in large pieces falling from the roof of the sewer tunnel. These concrete pieces are now sitting on the tunnel floor, collecting further silt and debris from the hundreds of thousands of litres of wastewater that passes through it each day.

Work is happening inside the sewer to restore it to its optimum condition. We have developed custom made machines that can be driven through the wastewater tunnel by our specialist workers to remove the debris. The walls and roof are gaining new life through the application of spray-on abrasion-resistant concrete.

The once-in-a-generation restoration works taking place inside the NSOOS are crucial for protecting Sydney Harbour and other waterways from sewage overflows and will extend the life of the structure by at least 50 years.

Repairs, Lane Cove to Northwood

The 2.5 kilometre section of NSOOS between Lane Cove River and Woodford Bay Reserve, Northwood was repaired and rehabilitated between 2017 and late 2021.

The work required access into the tunnel at the following locations:

Burns Bay Road, Lane Cove
Burns Bay Reserve, Riverview
St Ignatius College, Riverview
Tambourine Bay Road, Riverview
Warraroon Reserve, Longueville
Woodford Bay Reserve, Longueville / Northwood

All sites have been restored in consultation and agreement with Lane Cove Council.

Silt and debris removal, Northwood to Crows Nest (West Street)

The 3.1 kilometre section of NSOOS between Woodford Bay Reserve, Northwood and West Street, Crows Nest had silt and debris removed from inside the tunnel between 2021 and 2022.

The work involved access into the tunnel at the following locations:

Gore Creek Reserve (Bob Campbell Oval), Greenwich
Carlotta Street, Greenwich
Russell Street, Wollstonecraft
Carlyle Street, Wollstonecraft
West Street, Crows Nest

Silt and debris removal and repairs, Cremorne (Park Avenue) to Crows Nest (West Street)

The 1 kilometre section of NSOOS tunnel between Park Avenue, Cremorne and West Street, Crows Nest has been repaired and rehabilitated, with work completed in August 2023.

This work required access into the sewer tunnel at the following locations.

Park Avenue, Cremorne
Cammeray Golf Course
ANZAC Park, Cammeray

All sites have been restored in consultation and agreement with North Sydney Council.

Repairs, Cremorne (Brightmore Reserve) to Mosman (Spit)

The 2.7 kilometre section of NSOOS tunnel between Brightmore Reserve, Cremorne and The Spit, Mosman is currently being desilted, repaired and rehabilitated. The work requires access into the tunnel at the following locations:

Brightmore Reserve, Cremorne
Brothers Memorial Park, Cremorne
Quakers Hat Bay, Bay Street, Mosman
Upper Spit Road, Mosman
The Spit Syphon, off Parriwi Road, Mosman

All sites will be restored in consultation and agreement with North Sydney Council and Mosman Council. We expect this work to be completed by early 2027, weather and tunnel conditions permitting.