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Thames Tideway Tunnel

The River Thames is our most important water source. As the UK's largest water supplier, it's our responsibility to protect it. To achieve this, we're working on improving the sewage system.

One of the largest improvement projects to our network is the Thames Tideway Tunnel, or super sewer. Delivered by Tideway, this £4.5 billion project is a 25km tunnel running from west to east London. This is largely under the route of the River Thames.

The tunnel measures at 7.2m wide (the width of three London buses) and is up to 67m deep. This extra capacity will help the system cope with the growing population and environment.

It's part of a three-part London Tideway improvements scheme to improve river health.

thames tideway tunnel

How the tunnel will help the river and environment

Over the last 30 years, we've seen a dramatic clean-up of the Thames. The raw sewage that overspills each year is its last major source of pollution.

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

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.

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 7.2m diameter, 7km long tunnel. The tunnel runs from Abbey Mills pumping station. It then flows to Beckton sewage treatment works. 

The Lee Tunnel has already reduced sewage that would have previously polluted the River Lee. 

Third phase

Construction started in 2016 by a separate company called Bazalgette Tunnel Ltd. They're also known as Tideway. It's due to enter commissioning in 2024. It will begin to intercept CSOs along the River Thames from Acton in West London to Abbey Mills in East London. 

Once complete, the tunnel will operate with the sewage treatment works and the Lee Tunnel.

Funding the Thames Tideway Tunnel

Our wastewater customers are paying for the Thames Tideway Tunnel through their bills. Once completed, we will operate the tunnel as an integral part of the London sewerage network. Tideway will be responsible for its day-to-day maintenance.

Average annual household bills will rise by no more than £25 a year as a result of the project, before inflation. £1.1 billion of the construction cost is being funded directly by Thames Water.

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.