Tideway, the company responsible for delivering the Thames Tideway Tunnel, has announced the successful activation of the new super sewer, ushering in a healthier future for London’s iconic river.

After ten years of construction the last of 21 connections has been made between the original Victorian sewers and the new 25km Thames Tideway Tunnel, bringing the entire system online to protect the tidal Thames from sewage pollution.

Historically, the sewer network has struggled to cope with the twin challenges of population growth and climate change, with rainfall regularly overwhelming the system and causing it to discharge into the Thames.

With the new 25km storage and transfer sewer tunnel fully connected 95 per cent of those spills are now being stopped.

Connections have been made at landmark locations including the starting point of the University Boat Race at Putney Embankment; Chelsea and Victoria Embankments; Blackfriars Bridge in the heart of the City of London; and King Edward Memorial Park in Wapping.

Today, Tideway has published its latest data on sewage prevented from entering the river since it first started connecting the super sewer. 5,500,000m³ has been captured to date – the equivalent of 2,200 Olympic-sized swimming pools. Data updates will be published regularly via a new tracker at www.tideway.london

Tideway CEO Andy Mitchell said:

“This is another significant step forward – with this final connection complete, the super sewer is fully up and running and protecting the Thames. Our next step is to test it in storm conditions – which is why we are keeping a close eye on the weather – and we will do this over the coming months.

“We are at the start of a new chapter for London and its river. Our mission has always been about creating not just a tunnel, but a healthier, thriving environment for the river and its inhabitants. We look forward to seeing a real impact in the years to come and sharing everything we learn about the positive changes.”

The 25km-long super sewer connects to the 6.9km-long existing Lee Tunnel, a Thames Water asset – forming the London Tideway Tunnel (LTT) system.

The work of bringing the full system online began in the autumn of 2024, when Tideway announced that the first four connections had led to 589,000 tonnes of storm sewage being captured by the LTT in a single, rainy 24-hour period.

Later, in December, Tideway revealed that 848,365 tonnes had been captured during heavy rainfall in another 24-hour period – November 27th.

Work on the project began in 2016 – with activity taking place at two dozen construction sites from Acton in west London to Abbey Mills Pumping Station in Stratford, east London.

More than 20 deep shafts – some as wide as the dome of St Paul’s Cathedral – were constructed across London to divert sewage flows and to lower tunnelling machines into the ground.

The first of the giant machines started work deep beneath London in 2018, with primary tunnelling on the 25km main tunnel and two smaller connection tunnels completed in 2022.

By the autumn of 2023, a secondary tunnel lining was fully complete on all the tunnels, with the heavy civil engineering work then completed in the spring of 2024.

The Tideway project is being delivered by an alliance of contractors as follows:

• west region - joint venture of BAM Nuttall, Morgan Sindall Infrastructure and Balfour Beatty
• central region - joint venture of Ferrovial Agroman UK and Laing O'Rourke
• east region - joint venture of Costain, Vinci Construction Grands Projets and Bachy Soletanche

System integration is being delivered by Amey, which is responsible for providing process control, communication equipment and software systems for operation, maintenance and reporting across the Thames Tideway Tunnel system.

The project is on track to be fully complete (with testing complete) later this year. Thames Water will then operate the system, as part of its London wastewater network.

Steve Reed, Environment Secretary said:

“This Government is determined to clean up our polluted rivers, lakes and seas – and that includes the capital’s iconic Thames river.

“The Thames Tideway Tunnel is an example of the kind of infrastructure investment needed to clean up our waterways around the country and builds on this government’s wider ambition to boost national infrastructure under the Plan for Change.”

Chris Weston, Thames Water CEO commented:

"London’s Victorian sewer system was built for four million people but today, it serves over nine million. The final connection of the Thames Tideway Tunnel to our network is a major milestone in a three-stage programme to help London's wastewater system cope with a growing population and the impact of climate change.

"This infrastructure project, funded by Thames Water customers, will reduce sewage discharges into the Thames and create lasting benefits for biodiversity, recreation and public health. We know there is still much more to do so our focus now turns to the next phase of our work to continue cleaning up London’s rivers and watercourses.

The tunnel is fully constructed and being com-missioned with a project completion date of 2025.

In May 2024, the new tunnel was connected to the 7km Lee Tunnel, an existing Thames Water asset, which has been in operation since 2016 capturing more than five million cubic metres a year of sewage that would otherwise have flowed into the Channelsea Creek.

The combined system, now known as the London Tideway Tunnel (LTT), provides protection for the entire tidal Thames with a capacity of 1.6m m3.

David Black, Chief Executive of Ofwat added:

"This is an historic moment in the development of London's infrastructure – and we are proud to have worked with partners on the development, oversight and delivery of this scheme. The project demonstrates how the use of competitive models for delivery and innovation in finance arrangements can achieve good outcomes for customers and the environment alike.

"As Tideway moves towards full completion, we are already planning for the future and creating the foundations for future economic growth. By optimising our innovative regulatory models, including learnings from Tideway's financing structure, we will unlock investment for the next generation of major water and wastewater infrastructure projects."