Full Breakdown
Toxic Algae Prompt Swimming Ban at London’s First Thames Bathing Site
8/20/2026, 1:01:39 AM
Core Event
Swimmers have been warned to avoid the Ham and Kingston stretch of the River Thames after the Environment Agency (EA) detected a bloom of potentially toxic blue-green algae. The agency placed an “advice against bathing” notice on the SWIMINFO website and installed signage with the Royal Borough of Kingston upon Thames. Richmond Council also advised the public to stay out of the water and keep pets away. The bloom was identified in late August 2026, shortly after the site received official bathing-water designation in May 2026.
Background & Context
The Ham and Kingston location became London’s first officially designated bathing water under the EU Water Framework Directive in May 2026. Designation requires rigorous testing for faecal indicator organisms, but a full water-quality classification will not be issued until after the bathing season ends on 30 September 2026.
The site lies downstream of Thames Water’s Hogsmill sewage-treatment plant, three miles upstream. Thames Water is pursuing a £250 million water-recycling scheme that would abstract 75 million litres of river water per day during low-flow periods and replace it with treated effluent from the Mogden works via a new tunnel. The EA previously rejected a similar proposal, citing concerns that discharged treated sewage would raise river temperature, alter salinity, and harm fish and biodiversity. Thames Water has been in breach of its permit at the Hogsmill plant, discharging raw sewage unlawfully, and upgrades promised in 2025 are now unlikely before 2028.
Official Statements & Responses
The EA confirmed the presence of blue-green algae and warned that high concentrations can produce toxins harmful to humans, pets and wildlife. EA officials said they would collect additional water samples over the next 24 hours and keep the advisory notice in place until safety can be assured.
Thames Water’s spokesperson said the proposed Teddington direct-river abstraction project would meet EA standards and would not deteriorate water quality.
Richmond Council echoed the EA’s warning, urging visitors to avoid swimming and to keep dogs away from the water.
Criticism & Opposition
Local Liberal Democrat MP Munira Wilson, Kingston council and river-user groups have opposed the recycling scheme, arguing it would increase river temperature by at least 1 °C and place “extreme environmental pressure” on the Thames during droughts. Campaigners contend the scheme would provide only a fraction of the water needed while adding stress to an already polluted river.
On-the-Ground Reports
Marlene Lawrence, founder of the swimming group Teddington Bluetits, reported an itchy rash after contact with the water, which she attributed to the algae. She described the bloom as unusual for a moving river and linked its emergence to consecutive record-breaking heatwaves.
Conflicting Reports & Gaps
The EA has not yet completed its full assessment of toxin levels, and water-quality classification for the site remains pending until after 30 September 2026. Consequently, the precise health risk to swimmers cannot be definitively quantified at this stage.
What’s Next
The EA will continue sampling over the next 24 hours to map the bloom’s extent. A formal water-quality classification for the Ham and Kingston bathing site is scheduled for release after the bathing season ends on 30 September 2026. Ofwat’s investigation into Thames Water’s failure to upgrade the Hogsmill plant is ongoing, and the recycling scheme remains in the pre-application stage pending further regulatory review.
