At 25-kilometres long, The Thames Tideway Tunnel – otherwise known as London's 'super sewer' – is the UK's largest ever water infrastructure project and the most significant intervention to tackle sewage pollution in the River Thames in over 150 years.

In February 2025, after nearly a decade of construction by Tideway – the licensed infrastructure provider set up to finance, build, maintain and operate the Thames Tideway Tunnel – it was fully connected to the pre-existing Victorian sewer network.

By September, Tideway reported that more than 9.3 million cubic metres of waste had been prevented from entering the Thames, which over time is expected to dramatically improve water quality and safeguard aquatic life and public health.

The tunnel, along with Thames Water-operated Lee Tunnel and upgrades to various sewage treatment works, is designed to prevent 95 percent of sewage discharges from entering the river.

Beyond its environmental achievements, Tideway also broke new ground in sustainable finance. In July 2025, it became the first UK corporate to issue a blue bond in sterling, underscoring its role in protecting marine ecosystems and setting a precedent for water-focused investment.