Tipperary County Council are advising the public to exercise caution at Lough Derg following the discovery of the blue-green algae bloom which can produce harmful toxins.
It is easily recognisable with a bright pea-green paint colour and resembles a scum, on or close to the shoreline.
Contact with the bloom could cause skin irritation.
The council are warning people to keep all animals, especially dogs, away from the affected area and to ensure they have an alternative source of drinking water.
