The Ham bathing site on the Thames in south-west London was designated in May 2025 under the EU water framework directive — the first official bathing spot on the river in London. Within weeks, the Environment Agency posted signs warning swimmers and pets to stay out of the water. Blue-green algal blooms, rare in moving water, had colonised the site. The likely cause: extreme heat, low river flow, and nutrient pollution from sewage upstream. Thames Water's Hogsmill sewage treatment plant sits three miles upstream of Ham. The company has been in breach of its permit conditions at Hogsmill, meaning it has discharged raw sewage illegally. An upgrade promised for last year was among more than 100 projects the company postponed; the work is now unlikely before 2028. Ofwat is investigating. The algae outbreak lands directly on the doorstep of Thames Water's £250m Teddington Direct River Abstraction scheme, which would abstract 75m litres of water a day from the Thames during low flow and replace it with treated sewage from the nearby Mogden works via a new tunnel. The Environment Agency previously rejected the scheme because treated effluent would raise water temperature during low flow, alter salinity, and harm fish and biodiversity. The scheme has been redesignated a strategic infrastructure project, allowing it to bypass local authority opposition. The numbers tell their own story. Thames Water proposes to add 75 million litres of treated sewage daily to a river already under ecological stress. The company leaks 570 million litres of water every day — 7.6 times the volume the Teddington scheme would supply. It carries £20 billion in debt. The bathing designation that was supposed to force cleanup instead revealed how far the underlying systems have degraded. Local opposition is broad: Liberal Democrat MP Munira Wilson, the council, river users, and the Teddington Bluetits swimming group that secured the bathing designation all oppose the scheme. Marlene Lawrence of the Bluetits noted the algae appeared for the first time in nearly six years of swimming at Ham, calling it evidence the river is already under stress from drought and high temperatures. She warned the abstraction scheme would raise river temperature by at least 1°C. Thames Water's response follows a familiar pattern: reassurance without addressing the structural contradiction. The company claims the treated outfall would sit downstream of the bathing site, flowing over Teddington Weir into the tidal Thames. But the algae bloom is upstream, fed by the same sewage infrastructure the company has failed to maintain. The downstream-outfall argument is a geographic technicality layered over systemic neglect. The bathing water designation movement across England is designed to force exactly this kind of accountability — more rigorous testing, more pressure on water companies. At Ham, the mechanism worked faster than anyone expected. The designation didn't clean the river. It made the contamination visible.
