London's first Thames bathing site closed over toxic algae warning

Swimmers have been warned to avoid London’s first officially designated river bathing water after a toxic algal bloom was identified on the River Thames. The Environment Agency issued a formal notice on August 18, 2026, advising against bathing at the Ham and Kingston site due to pollution from harmful blue-green algae, technically known as cyanobacteria. The nontidal stretch of the Thames, which only received its bathing water status in May, has now been closed to swimmers.

The warning comes after Marlene Lawrence, a swimmer who helped campaign for the site’s designation, noticed signs of algae last week. Lawrence, founder of the local group Teddington Bluetits, swam in the river before the official notice was posted and reported an immediate physical reaction. “Instantly on Sunday night I came out in a really bad rash, itchy spots, and that’s not like me,” she said. “I can only attribute it to the algae in the river.” Lawrence and fellow swimmers had never previously encountered a blue-green algae bloom at this location.

An Environment Agency spokesperson confirmed the agency had identified blue-green algae on the lower River Thames, including the Ham and Kingston site. The...