Toxic algae closes Ham and Kingston Thames bathing site after three months
Environment Agency warns against swimming or letting pets enter the water until further notice
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The Ham and Kingston stretch of the River Thames, designated London’s first official bathing site in May 2026, has been closed to swimmers and pets after the Environment Agency detected a bloom of toxic blue-green algae. Richmond Council issued the warning on 19 August, advising visitors to avoid contact with the water and visible algae near the riverbank.
The closure affects the area between the Half Mile Tree and the YMCA Hawker Centre, which opened to the public in mid-May. The site has not yet received its first water quality classification, with results due after the bathing season ends on 30 September. The Environment Agency will take further water samples over the next 24 hours to assess the extent of the bloom.
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Sewage discharges and drought plans under scrutiny
Campaigners from Save Our Lands and River (SOLAR) have raised concerns about the algae bloom, linking it to sewage discharges from Hogsmill Sewage Treatment Works, located three miles upstream. The Environment Agency found the plant in breach of its environmental permit in May 2026, citing inadequate storm sewage storage among the violations.
It’s deeply concerning, but sadly not surprising, that London’s new bathing site at Ham and Kingston has been hit by a toxic algae warning just weeks after opening.
Ian McNuff, SOLAR campaigner
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The algae discovery has intensified opposition to Thames Water’s Teddington Direct River Abstraction project, which proposes replacing up to 75 million litres of river water daily with treated wastewater during droughts. The £250m scheme would abstract water from the Thames above Teddington Weir and replace it with effluent from Mogden Sewage Treatment Works, via a new tunnel.
Thames Water has stated the treated wastewater would be released downstream of the bathing site, flowing over Teddington Weir into the tidal Thames. The company said the project would meet strict environmental standards set by the Environment Agency. However, the agency previously rejected an earlier version of the scheme, citing risks to fish and biodiversity from changes in water temperature and salinity.
Campaigners demand stricter wastewater standards
SOLAR has launched a petition calling for all new wastewater treatment infrastructure to meet stricter standards, including a fourth stage of treatment to remove micropollutants. The petition, which has gathered over 42,850 signatures, needs 100,000 by 1 November 2026 to be considered for a parliamentary debate.
Marlene Lawrence, a member of the swimming group Teddington Bluetits, which successfully applied for the bathing water designation, said the algae bloom was unprecedented in her six years of swimming at the site. She attributed the bloom to low river flow and high temperatures, warning that climate change could make such events more frequent.
Thames Water has postponed upgrades to Hogsmill Sewage Treatment Works until at least 2028, despite the plant’s permit breaches. The company, which is £20bn in debt, has delayed over 100 environmental projects, prompting an investigation by the water regulator Ofwat.
What happens next
The Environment Agency will continue monitoring the algae bloom and water quality at the Ham and Kingston site. The bathing water classification, based on samples taken during the 2026 season, will be published after 30 September. Thames Water’s Teddington Direct River Abstraction project remains in the pre-application stage for a development consent order.
Residents can respond by signing SOLAR’s petition or submitting comments during the public consultation phase of Thames Water’s project, which has not yet been scheduled. Richmond Council has not announced any additional measures beyond the current advisory notices.
Questions this report answers
+Why has the Ham and Kingston bathing site been closed?
The Environment Agency found toxic blue-green algae in the water, which can produce harmful toxins. Richmond Council and the agency have advised against swimming or letting pets enter the water until further notice.
+How long will the bathing site remain closed?
It is unclear how long the closure will last. The Environment Agency is taking further water samples and will continue monitoring the algae bloom. No reopening date has been set.
+What is Thames Water’s Teddington Direct River Abstraction project?
The £250m project proposes replacing up to 75 million litres of river water daily with treated wastewater during droughts. Thames Water says the treated water would be released downstream of the bathing site.
+How can residents respond to the algae bloom or Thames Water’s plans?
Residents can sign SOLAR’s petition demanding stricter wastewater treatment standards. They can also participate in future public consultations on Thames Water’s project, though no dates have been announced.
News London Desk
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