Tideway super sewer cut raw sewage into the Thames by 86% in its first year

Raw sewage reaching the tidal Thames in London fell by 86% in 2025, the first year of the Thames Tideway Tunnel, compared with the previous average, a Thames Water report has found.

Roughly 84 tonnes of rubbish, including wet wipes and sanitary products, was also kept out of the river by the tunnel. Thames Water, which now runs it, counted 269 days of higher health risk linked to sewage overflows in 2023. In 2025 there were 38.

How the Thames Tideway Tunnel works

The 16-mile (26km) pipe lies deep below ground, linking Acton with Abbey Mills. At 7.2m (23ft) wide, it can hold the equivalent of 600 Olympic-sized swimming pools. The waste it holds is pumped on to the large sewage treatment works at Beckton.

It was built to add capacity, so that more rainwater and waste can be held back instead of overflowing into the tidal river. That stretch of the Thames was once declared “biologically dead”. Thames Water now describes it as “on the road to recovery”, and the report found conditions for fish and other wildlife had improved since the tunnel began working.

Tess Fayers, Thames Water’s director of waste and bioresources, called the results “an important milestone for the river”.

Pollution and climate change still a risk for the Thames

The report warns that pollution and climate change remain “big challenges” and says further action is needed.

Thames21, a charity that campaigns for healthier waterways, called the tunnel “an impressive piece of engineering”. It said other ways of managing water would be needed if climate change makes extreme weather more frequent. Its chief executive, Chris Coode, wants more money put into nature-based solutions, such as wetlands to clean up polluting outfalls and raingardens to deal with surface water flooding.