Thames Tideway Tunnel
The River Thames is one of our most important water sources, and as the UK’s largest water supplier, we have a responsibility to help protect it. One way we're doing this is by supporting improvements to London’s sewerage system.
A key part of this is the Thames Tideway Tunnel, also known as the super sewer. Operated by Thames Water, the 25km tunnel runs from west to east London, largely beneath the River Thames. This £4.6 billion project was delivered and is owned and maintained by Tideway.
The tunnel is roughly the width of three London buses and reaches depths of up to 67 metres. This additional capacity will help the sewerage network better manage the demands of a growing population and changing environmental pressures.
It's part of a three-part London Tideway improvements scheme designed to improve the health of the River Thames.
Image credit: Tideway (Bazalgette Tunnel Limited)
How the tunnel will help the river and environment
The Thames Tideway Tunnel will help to:
Reduce combined sewer overflows (CSOs) in a typical year by 95%.
Collect sewage so it can be treated before entering the river.
Provide habitats for a range of aquatic wildlife in the area.
Decrease over fifty sewage spills a year to around five. These will mostly contain surface water runoff after heavy storms.
Reduce the amount of sewage-related litter in the Thames. This will also decrease the amount ingested by wildlife.
Capture the ‘first flush’ from the sewers after heavy rain. This contains sediment built-up during periods of dry weather.
Protect our river's health and improve the appearance of the river.
Provide a clean, rich, and diverse ecology for London.
Generate more renewable energy using collected sewage waste.
Timeline of work
How this project has progressed.
Prior work
The plan for the London Tideway Improvements was created by the Thames Tideway Strategic Study. This was in the early 2000s.
First phase
We upgraded five Thames Water sites in 2014. This included Beckton, Crossness, Riverside, Long Reach and Mogden. These works, on average, have stopped over 40 million tonnes of sewage being discharged into the Thames every year. *
Second phase
In 2016, we built the Lee Tunnel. It intercepts the tidal Thames' largest combined sewer overflow (CSO) at Abbey Mills. The Lee Tunnel is a 7km long tunnel that runs from Abbey Mills pumping station to Beckton sewage treatment works.
The Lee Tunnel has captured over 5 million tonnes of sewage every year that would have previously discharged into the River Lee. **
Third phase
A new company dedicated to building the Thames Tideway Tunnel was set up. Bazalgette Tunnel Ltd, known as Tideway, started construction in 2016. In May 2024, the new 25km super sewer was connected to the Lee Tunnel. This completed the full ‘London Tideway Tunnel’ network.
We have spent 1.1bn to support Tideway in the delivery of the project.
The new tunnel operates with the sewage treatment works and the Lee Tunnel. Together this new combined system has a combined capacity of 1.6m m3 to protect the River Thames in London.
The Thames Tideway Tunnel has now begun intercepting CSOs along the river.
* Stats taken as an average from annual averages over 5 years (2016-2020 compared to 2009 to 2012)
** Stats taken as an average from annual averages over 5 years (2017-2021)
Funding the Thames Tideway Tunnel
Our wastewater customers are paying for the Thames Tideway Tunnel through their bills.
Average annual household bills will rise by no more than £25 a year as a result of the project, before inflation. An additional £2.5 billion has been invested by Thames Water for all three phases of this scheme.
Surveying the area
Since the Lee Tunnel has been completed, results found water quality in the area is improving.
The survey carried out on the Channelsea River also showed 14 species of fish. This indicates the river is healthy and supports a wide variety of fish and other wildlife. It can be considered a good quality urban river system.
Other investment projects
Take a look at our other investment projects to see what else we’re doing to improve our network and waterways.