Thames Tideway Tunnel cuts sewage spills by 86% in first year
The 16-mile super sewer has also prevented 84 tonnes of litter from entering the river.
Trust 42Craft 61Hype 20How this was reported ▾
The central claim is attributed to Thames Water, with a quote from a named conservation expert.
How well corroborated and evidenced the reporting is. Higher is better.
The report explains why the super sewer matters, names specific figures and dates, and includes a quote from an affected party.
Context, balance and separation of fact from comment. Higher is better.
The language used is measured and proportionate, with no sensationalism or manufactured urgency.
How far presentation runs ahead of substance. Lower is better.
1 source assessed · methodology
The health of the River Thames has seen a significant improvement in 2025, the first full year of operation for the Thames Tideway Tunnel, commonly known as the super sewer. Thames Water reported an 86% reduction in raw sewage entering the river compared to previous averages. The new infrastructure also intercepted approximately 84 tonnes of litter, including items like wet wipes and sanitary products, preventing them from reaching the waterway.
The tunnel was constructed to increase the capacity for storing rainwater and waste, thereby reducing the frequency of overflows into the tidal Thames. Despite these improvements, Thames Water's report acknowledged that pollution and climate change continue to pose substantial challenges, necessitating ongoing efforts to maintain the river's health.
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Tunnel specifications and impact
The 16-mile (26km) Thames Tideway Tunnel runs underground from Acton in west London to Abbey Mills in the east. With a width of 7.2 metres, it has the capacity to store the equivalent of 600 Olympic-sized swimming pools of liquid. This stored material is then pumped to the sewage treatment works in Beckton, east London. Thames Water, which now manages the tunnel, stated that river users can expect increased confidence in water-based activities.
The company's assessment of the tunnel's environmental benefits revealed a dramatic decrease in days with elevated health risks due to sewage overflows. These days fell from 269 in 2023 to just 38 in 2025. Thames Water described the river, once considered biologically inactive, as now being 'on the road to recovery'. Conditions for fish and other aquatic wildlife in the tidal Thames have also reportedly improved since the super sewer became operational.
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While there is still work to do, it is encouraging to see the progress being made in diverting untreated sewage away from the Thames, reducing risks to this vital ecosystem and the wildlife and people that depend on it.
Alison Debney, Zoological Society of London
Alison Debney, a lead for conservation recovery at the Zoological Society of London, commented that continued investment and innovation are essential for preventing further pollution and safeguarding the long-term health of the Thames for both nature and the public.
Questions this report answers
+How much has raw sewage entering the River Thames been reduced?
In 2025, the first full year of the Thames Tideway Tunnel's operation, raw sewage entering the River Thames was reduced by 86% compared to previous averages. This significant reduction contributes to the overall improvement of the river's health.
+How much litter has the super sewer prevented from reaching the river?
The Thames Tideway Tunnel prevented approximately 84 tonnes of litter from reaching the River Thames in 2025. This litter included items such as wet wipes and sanitary products, which can harm aquatic ecosystems.
+How has the number of health risk days from sewage overflows changed?
The number of days with increased health risks linked to sewage overflows has dramatically decreased. In 2023, there were 269 such days, which fell to 38 days in 2025, following the operational start of the Thames Tideway Tunnel.
+What are the dimensions and capacity of the Thames Tideway Tunnel?
The Thames Tideway Tunnel is 16 miles long and 7.2 metres wide. It has the capacity to store the equivalent of 600 Olympic-sized swimming pools of liquid, which is then transferred for treatment.
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