• First 4 of 21 sites switched on, with new tunnel starting to protect River Thames from sewage pollution for the first time 

• First data records half a million cubic metres of sewage captured by the tunnel network in 24-hour period

• Teams now working to bring system into full operation – with project on track for completion in 2025 

London’s super sewer, designed to protect the River Thames from sewage pollution well into the future, has now been turned on. 

In May 2024, the new 25km super sewer was connected to the 6.9km Lee Tunnel – completing the full ‘London Tideway Tunnel’ network, which has a combined capacity of 1.6m m³ to protect the River Thames in London.

And data published today shows that in one day alone, when London saw heavy rainfall on September 23rd, 589,000 m³ was captured by the London Tideway Tunnel with just the first connections activated.   

Valves, which operate like giant gates, are now open at 4 of the 21 locations that make up the system, with the rest due to come online in the coming months, when the sewer will reach full operating capacity.   

Tideway CEO Andy Mitchell said: “This is an important moment for the Thames. The super sewer has been switched on and is starting to protect the river from sewage pollution.  

“After eight years of construction, in which almost 25,000 people have contributed more than 40 million working hours, this system is operating for the first time. 

“These are early days, with more connections to make and further testing to come, but the super sewer’s positive influence on the health of the Thames will increase over the coming months – and London will soon be home to the cleaner, healthier river it deserves.” 

The new system will have a capacity equivalent to 640 Olympic-sized swimming pools.  

Teams are now working to bring the system into full operation. This involves connecting the remaining discharge points to the new super sewer and testing the entire system during different weather conditions, including heavy storms. 

While the testing phase is now underway, work continues above ground to finish the new riverside public spaces being created as part of the project.  

The first of these was opened to the public last year, next to Putney Bridge. Teams are now working across London – from Chelsea to Wapping – to finish off the remaining six public spaces.  

Once fully operational, Tideway anticipates that the super sewer will virtually eliminate the harmful effects of sewage pollution on the River Thames through central London. 

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

By the autumn of 2023, secondary 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. The west region is being delivered by a joint venture of BAM Nuttall, Morgan Sindall Infrastructure and Balfour Beatty. The central region is being delivered by a joint venture of Ferrovial Agroman UK and Laing O'Rourke. The east region is being delivered by a 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 due to be fully up and running (with testing complete) in 2025. Thames Water will then operate the system, as part of its London wastewater network. 

Chris Weston, CEO of Thames Water said: “This is a very exciting moment for us all as we see the third and final phase of the huge scheme to help prevent sewage pollution entering the River Thames. We recognise no single body has the ability to achieve this vision alone and are keen to continue our work with partners to meet expectations of the community and the environment.

“The Thames Tideway Tunnel, a £4.5bn investment made by our customers, is nearing completion. We are already seeing the benefits of our £700m investment in Lee Tunnel in 2016, and the Channelsea River and River Lea now have ‘good to excellent’ water quality as a result – showing how the Thames Tideway Tunnel is set to bring further improvements in central London.

“We have published plans to upgrade over 250 of our sewage treatment works. In London, we have started the £100m upgrade of Mogden sewage treatment works, and we’re also spending £145m upgrading Beckton sewage treatment works, which will increase capacity and reduce the number of storm discharges.”

Chris Coode, CEO of river charity Thames21, said: "We are delighted to see the Thames Tideway Tunnel is coming into commission. This critical infrastructure will play a significant role in protecting the tidal Thames from the damage caused by sewage pollution, a step toward improving the health of the river in central London.

“We hope this major project will inspire the rapid implementation of other solutions, to restore and protect our rivers. Much work remains to be done across the wider Thames Basin to address the full range of sewage challenges."

Water Minister Emma Hardy said: “The Thames has defined the capital and the nation, but like so many of our waterways it has been degraded by unacceptable levels of pollution.

“Our reforms of the water sector will fundamentally change how our water system works and clean up our waterways. The Thames Tideway Tunnel is an example of the transformation and investment we want to see up and down the country to clean up our rivers, lakes and seas.

“This is an important milestone with the first sections in action and already reducing the level of sewage pollution in the Thames.”

Environment Agency Chair Alan Lovell said: “We are proud to have worked collaboratively with partners on the Tideway project reducing storm sewage spills into the tidal Thames by around 95%. 

“Our contribution ensures that the best possible environmental outcomes are achieved; we are confident that the project will markedly improve the river for wildlife and for people.

“We are regulating the system with environmental permits and will continue to monitor water quality and aquatic life in our capital’s river.

Tideway is the company responsible for delivering the Thames Tideway Tunnel, a new 25km storage and transfer sewer tunnel. The tunnel is fully constructed and being commissioned 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. This combined system, now known as the London Tideway Tunnel (LTT), provides protection for the entire tidal Thames with a capacity of 1.6m m³. 

Data published today shows that in one day alone, when London saw heavy rainfall on September 23rd, 589,000 m³ was captured with just the first connections activated preventing 219,000m³ from entering the Thames, with the existing Thames Water Lee Tunnel capturing 370,000m³.