All water activities, including paddle boarding, have been suspended with immediate effect at Pen y Fan Pond.
The decision was announced by Caerphilly Council on Friday, August 7, after blue-green algae was found at the lake, which is near Oakdale.
Water activities had returned to the pond on Wednesday, August 5, and Caerphilly Adventures – the group which runs activities in the county – had reported unprecedented demand for activities such as paddle boarding.
Blue-green algae, also known as cyanobacteria, occurs naturally in rivers, streams and lakes and can multiply and form ‘blooms’ during periods of hot weather.
The algae can produce toxins harmful to both humans and animals, causing rashes and irritation.
The RSPCA and the British Veterinary Association have both reported deaths to animals associated with blue-green algae, including pets.
In a statement, Caerphilly County Borough Council advised residents to ensure pets do not enter the pond, adding those that do should be washed with clean water before seeking precautionary advice from a qualified vet.
Councillor Nigel George, cabinet member for the environment, said: “This advice certainly isn’t intended to cause undue concern and worry, however it is important that no recreational activities, including fishing or public access takes place.
“Signage has been placed around the pond and regular inspections of the body of water will continue to take place. We will continue to work alongside Natural Resources Wales to address this issue”.
The discovery follows a plea from Newport City Council on Thursday, August 6, urging visitors not to come into contact with water at Fourteen Locks Canal Centre near Rogerstone after blue-green algae was also found there.
Newport City Council has also urged people not to allow their pets to have contact with water along the Monmouthshire and Brecon Canal, which runs through Risca and Crosskeys.
The council has not reported any people or pets feeling unwell following use of the lake this week, and it is not currently known how long activities will be postponed.
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