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Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →London’s Thames Tideway Tunnel—the “super sewer”—became fully connected to the existing sewer network in February 2025, when the final of 21 connections was made. That milestone followed the completion of underground construction in 2024; the network’s later move to full-capacity operation was a separate update, announced by Tideway in June 2026.
What is London’s “super sewer”?
The Thames Tideway Tunnel is a major wastewater infrastructure project built to intercept storm sewage that would otherwise overflow into the tidal Thames when London’s existing sewer system is overwhelmed. The captured sewage is carried through tunnels for treatment.
Tideway describes a 25 km main tunnel with a diameter of 7.2 metres. It connects to the existing Lee Tunnel, forming part of the wider London Tideway Tunnels system, whose stated storage capacity is 1.6 million cubic metres. These are project specifications published by Tideway.
When was the tunnel completed?
“Complete” refers to more than one project milestone. Tideway was established in 2015 to deliver the project, and work began in 2016. Underground construction reached its milestone in 2024, but commissioning and connection to the existing network continued after that. The first connection to the Lee Tunnel in 2024 began commissioning and early operation.
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In February 2025, Tideway announced that the final of 21 connections had been made, making the new tunnel fully connected to the existing system. In June 2026, Tideway announced that the network had begun operating at full capacity. The distinction matters: construction completion, full connection and full-capacity operation were successive stages, not one event. Tideway’s announcements describe the final connection and the later full-capacity milestone.
How does it help keep sewage out of the Thames?
During heavy rainfall, the existing sewer system can be overwhelmed, leading to storm sewage overflowing into the tidal river. The Tideway Tunnel is designed to intercept those overflows, hold the sewage in the tunnel network and convey it onward for treatment. Its connection to the Lee Tunnel is part of that wider system rather than a separate, isolated pipe.
The purpose is to reduce sewage discharges to the river. Capture totals show material diverted into the network; they do not, by themselves, establish a measured improvement in water quality, biodiversity or overall river health.
What capture figures has Tideway reported?
Tideway has published cumulative capture figures at different dates, using different units and reporting periods. They should be read as company-reported operational totals, not as independent evaluations of environmental outcomes.
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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errors| Reporting date | Tideway-reported figure | What it describes |
|---|---|---|
| February 2025 | 5.5 million cubic metres, which Tideway equated to 2,200 Olympic-sized swimming pools | Captured by the announcement of the final connection. Tideway, February 2025. |
| June 2025 | More than seven million tonnes | Sewage pollution captured to date, as reported in Tideway’s annual-report announcement. Tideway, June 2025. |
| June 2026 | More than 20 million tonnes | Storm sewage intercepted since the first connection in August 2024. Tideway, June 2026. |
The figures are not directly interchangeable: the February 2025 figure is a volume in cubic metres, while the later figures are in tonnes. No conversion between those units is established by these announcements.
What did the project cost, and how long is it designed to last?
In its June 2026 announcement, Tideway gave a project cost estimate of £4.6 billion and said water bills remained within the original estimated range of £20–£25 per year. The project-cost estimate and annual bill estimate describe different things; the bill figure is not the project’s total cost.
Tideway also stated that the tunnel network is designed to protect the Thames for at least 120 years. These cost, bill and design-life figures are Tideway’s claims in its June 2026 announcement.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What does completion establish—and what does it not?
The February 2025 milestone established that all 21 connections had been made between the new tunnel and the existing sewer network. Tideway’s later June 2026 announcement established that the network was operating at full capacity and reported its cumulative interception total since the first connection. Those facts describe project status and reported capture, not a quantified, independently measured ecological recovery of the Thames.
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In February 2025, 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.” That statement belongs to the commissioning context at the time; it is not a description of the network’s current status.
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