London’s super sewer sharply reduces sewage reaching the Thames

London’s new super sewer is keeping much more sewage out of the River Thames, bringing cleaner water for wildlife and the people who enjoy the river.

The first annual assessment estimates that storm overflow volumes fell 86% in 2025, compared with the average before the Thames Tideway Tunnel. It also estimates that the tunnel intercepted 84 tonnes of litter, including wet wipes.

The underground system stores rainwater and wastewater that would otherwise overflow into the tidal river, then transfers it for treatment at Beckton.

Thames21’s foreshore monitoring offers another sign of change: sewage-related items fell from 30% of recorded litter before operation to 18% in 2025.

These are early results, and the overflow figures are modelled. Unusually dry weather also helped. Thames21 says wetlands and rain gardens are still needed to manage heavier rainfall as the climate changes.

The tunnel cannot solve every pollution problem, but keeping waste out of the river gives wildlife and the people who enjoy the Thames a cleaner shared environment.

Sources

• BBC News — Super sewer is cleaning up the Thames, says report
• Thames Water — First annual Tideway benefits assessment