Blue-green algae are tiny organisms which develop naturally in lochs, ponds, reservoirs, rivers and in the sea. They are a common seasonal occurrence and waters which have been affected by agricultural, domestic or industrial discharges are more at risk of developing the algae.

In still waters the algae can multiply during the summer months and discolour the water which then appears green, blue-green or greenish brown and, occasionally, they clump together to form a scum on the surface of the water. At the shoreline, algal crusts may appear brown to almost black in colour.

Humans and animals can suffer as a result of direct contact with water affected by blue-green algae and NHS Tayside is advising the public, especially those who enjoy water sports, anglers and dog owners, to be alert to the blooms as temperatures rise.

"We routinely monitor levels of blue-green algae over the warmer months because of the potential health risk to people and to animals," explained Dr Julie Cavanagh, consultant in public health medicine for NHS Tayside.

"Canoeists, wind surfers and swimmers who come into contact with the algal scum or who accidentally swallow affected water can suffer from complaints such as skin rashes, eye irritation, vomiting, diarrhoea, or pains in muscles and joints, which are usually mild, but in some cases, can be severe."

"The risk to animals like dogs is significant over the summer months as they tend to drink more water in the heat and may eat shoreline algal crusts, so dog owners should keep an eye on their pets, especially if they live, or are walking, near water which could be affected.

"The public should be reassured that public drinking water supplies are treated to prevent any harmful effects to health from blue-green algae."

The Tayside waters which will be monitored for blue-green algal blooms this summer are: Monikie Ponds, Forfar Loch, Rescobie Loch, Clatto Reservoir, Lintrathen Reservoir, Backwater Reservoir, Loch Turret, Loch Lee, Glenogil Reservoir and Den of Ogil Reservoir.

Loch Leven has permanent notices displayed advising the public about the appearance and risks of algal blooms.

Where monitoring reveals higher than acceptable levels of algal bloom, warning notices will be posted at the affected waterways.

Monitoring in Tayside has already identified algal blooms in some of the area's watercourses this year, and at the moment warning notices have been erected at Clatto Reservoir.

Anyone who finds a loch, pond or river which they suspect is affected by blue-green algae and which is not displaying a warning sign, should contact their local environmental health service.