Swimmers have been warned to avoid London's first official bathing spot due to toxic algae – with dog owners also told it's "vitally important" to keep their pets away.
The Ham and Kingston site, in Kingston upon Thames, opened about three months ago and has been subject to regular water tests during the summer season, scheduled until the end of September.
It was included in the latest tranche of new spots for open water swimming in England announced by the government in May.
But the Environment Agency has now issued a warning advising people not to swim at the site due to the presence of blue-green algae, which can produce toxins that are harmful to humans and animals.
Officials said blue-green algae, or cyanobacteria, blooms when warm temperatures, low rainfall and calmer water conditions create ideal growing conditions.
The toxins produced can kill wild animals, farm animals and pets, and can also harm people, causing skin rashes and illness if swallowed.
An Environment Agency spokesperson said: "We have identified blue-green algae on the lower River Thames including the Ham and Kingston designated bathing water.
"We are working with the Royal Borough of Kingston upon Thames, who have put signage in this location to warn people that it is not safe to swim.
"An advice against bathing notice has been activated on the Swimfo website."
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It's also likely the section of the River Thames between Hampton and Kingston had also been affected, the spokesperson added.
"It is important that members of the public do not enter the Thames along this stretch," they warned. "It is also vitally important to keep dogs out of the water."
The Environment Agency is taking water samples along the stretch of river to confirm the extent of the algal bloom.
It said it has informed abstractors downstream and the UK Health Security Agency.
(c) Sky News 2026: Swimmers told to avoid London's only Thames bathing spot due to 'toxic algae'
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