Visitors to Clatto Reservoir in Dundee have been warned to avoid contact with the water.
Recent sampling has identified high levels of blue-green algae and until the all clear is given people are being asked to 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 can cause skin rashes. More serious health effects can include stomach upsets, eye irritations and pain in muscles and joints. These symptoms are usually mild, but in some cases can be severe.
If anyone has been in contact with the water and experiences health problems they should contact their GP or else NHS 24 on 111.
Notices have been posted at the reservoir.
Dundee City Council's Neighbourhood Services can provide further information on the algae on 433710.