London’s super sewer now in full flow
London’s new super sewer is now fully connected, ushering in a healthier future for the River Thames.
Construction of the 25km Thames Tideway Tunnel began almost 10 years ago. In February 2025, the last of 21 connections was made between the city’s original Victorian sewers and the new tunnel.
Historically, the city’s sewer network, which handled sewage and rainwater, had struggled to cope with the growing population and more extreme weather. This meant rainfall regularly overwhelmed the system, causing sewage to spill into the Thames.
The new system has already stopped 5.5m tonnes of sewage from entering the river, according to the company behind it, and will stop 95% of future spills.
"Our mission has always been about creating a healthier, thriving environment for the river and its inhabitants."
Tideway chief executive 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.”
Work on the project began in 2016, with activity taking place at two dozen construction sites. More than 20 deep shafts – some as wide as the dome of St Paul’s Cathedral – were built across London to divert sewage flows and to lower tunnelling machines into the ground.
The first of these machines started work beneath London in 2018, with all heavy civil engineering work wrapping up in the spring of 2024. The system is on track to fully complete in 2025, once testing completes. It will then be operated by Thames Water, as part of London’s wastewater network.
Mayor of London Sadiq Khan said: “This is an important milestone, which will mean a huge reduction in sewage going into the tidal Thames.
"We must now build on this work to go further and tackle the other sources of pollution damaging London’s waterways. I’m determined to make our rivers cleaner, safer and more accessible so that Londoners can enjoy the benefits of nature as we continue to build a greener and better city for all.”
Tideway regularly publishes latest data on volumes of sewage prevented from entering the river since it first started connecting the super sewer. To date, 5,500,000m³ has been – the equivalent of 2,200 Olympic-sized swimming pools. Data updates will be published online regularly via a new tracker at www.tideway.london