Britain Just Built a £4.5bn Super Sewer Under London — Here's What It Caught in Year One

Far below the London Underground, a 25 km tunnel now runs beneath the River Thames, from Acton in the west to Abbey Mills in the east. It is 7.2 metres wide, up to about 70 metres deep, and it does not carry trains. It carries sewage. For more than a century, heavy rain sent raw sewage from London's Victorian sewers straight into the Thames, by design. In its first full year, the Thames Tideway Tunnel caught more than 18 million tonnes of it. This video tells the story from the Great Stink of 1858 and Joseph Bazalgette's sewers to the "super sewer" that finally gives them somewhere to overflow other than the river, and the five problems the engineers had to beat: the ground under London, a city with no room to work, the drop to the bottom, the storm itself, and the bill. It also covers what the tunnel does not do: it intercepts the 34 most polluting overflows on the tidal Thames, not every source of pollution, and the cost rose from early estimates under £2bn to around £4.5bn. Chapters: 0:00 A tunnel most Londoners will never see 1:10 The honest part 2:05 The Great Stink of 1858 2:54 Joseph Bazalgette 4:03 The flaw built in on purpose 5:05 The plan: Lee Tunnel and Tideway 5:55 #5 The ground 6:51 #4 The city 7:43 #3 The drop 8:33 #2 The storm 9:25 #1 The bill 10:12 Year one: 18 million tonnes 11:11 The number: 120 11:44 How the pieces fit 12:03 What comes next Sources: Tideway: "London super sewer captures four and a half Wembley Stadiums' worth of sewage in first year" (February 2026) Tideway: Annual Report 2025–26 press release (June 2026) Tideway factsheet (September 2024): length, depth, capacity, spoil, river transport Thames Tideway Tunnel and Lee Tunnel: project history, costs, overflows (Wikipedia summary of Thames Water / Ofwat documents) Great Stink of 1858 and the Metropolitan Board of Works sewer system Tideway / Balfour Beatty: vortex drop shaft at Hammersmith (2020) Figures and timelines are as of October 2026. #Tideway #SuperSewer #London #Thames #Engineering