Visitors to Stobsmuir Ponds in Dundee have been warned to avoid contact with the water.
Recent sampling of the lower pond has identified high levels of blue-green algae and until the all clear is given people are being asked avoid contact with the water and keep their pets away.
When in high concentrations in the water this naturally occurring algae can multiply to cause algal blooms which may then release toxins. The behaviour of algae is erratic and the levels of its toxicity can fluctuate. It can appear one day, be dispersed by the wind and re-accumulate at any time.
Contact with algal scum or water close to it has been known to cause skin problems. More serious health effects can include stomach upsets, eye irritations, fever and pains in muscles and joints.
If anyone has been in contact with the water and experiences health problems they should contact NHS 24 on 08454 242424 or their GP.
Notices have been posted at the ponds.
A spokesman for Dundee City Council said: “Due to the high concentrations of blue green algae, parents are advised to be vigilant with their children and dog owners should prevent their dogs from drinking the water
"Officers will continue to monitor the quality of the water and notices will be removed when the hazard has passed."
Dundee City Council's environment department can provide further information on the algae on 436260.