A toxic invader is becoming a growing problem for nature-lovers at a Leeds beauty spot.
The waters at Yeadon Tarn are out of bounds to local sailing clubs and activity groups after toxic blue-green algae was spotted at the site.
The algae can be harmful to humans and could kill wild animals, livestock and domestic pets.
Warnings from Leeds City Council and the Environment Agency have been put up around Tarnfield Park advising people to keep away from the blooms and affected waters.
If the toxic algae make contact with humans it could cause rashes after skin contact and illnesses if swallowed.
Local groups who use the site will have to carry out risk assessments after they were warned about the dangers of the blooms and surrounding waters.
Activities at Leeds Sailing and Activity Centre have been stopped until the algae has disappeared.
Local councillor Ryk Downes (Lib Dem, Otley and Yeadon) said that he hoped the Tarn would re-open as soon as possible.
He said : “It is sad that the popular Tarn is currently out of use but thankfully, due to the prompt action of a council officer, we have been able to put precautionary measures in place quickly.
“I hope that a swift solution can be found so that we can get Yeadon Tarn open to the public again as soon as possible.”
A spokeswoman from Leeds City Council said that samples of water from the Tarn will continue to be taken to monitor the algae.
She said that the Tarn would be open again once the water has been clear for at least two weeks.
An Environment Agency spokesman said: “We have tested samples from Yeadon Tarn and can confirm the presence of toxic blue-green algae.
“Our advice is that people and animals should keep well away until the problem is resolved.
“We have informed Yeadon tarn management, local user groups and Leeds City Council of the situation.”
The Environment Agency were called to investigate the Tarn two years ago after a spate of fish deaths caused by a shortage of oxygen in the water.