Shetland Islands Council’s environmental health team has received notification that the Loch of North House near Twatt, Bixter contains blue-green algae.
Signs will be erected next to the loch warning that contact with algal scum should be avoided and for animals not to drink or enter the water.
Adjoining landowners have been advised of the situation, as have NHS Shetland and Shetland Angling Association.
Blue-green algae exist in fresh waters and can collect to form blooms looking like blue-green paint, in the water or on the shore line.
Blue-green algae can be toxic and give rise to adverse medical effects, include skin rashes, eye irritations, vomiting and diarrhoea, and fever and pains in muscles and joints.
Toxic algae have caused deaths of livestock and dogs.
The treatment of water supplies removes blue-green algae and additional treatment may be applied to destroy or remove toxins should they arise. The actions currently taken are precautionary.
Anyone who suspects blue-green algae at other locations are being asked to submit a notification to the council via the “Bloomin’ Algae” app.