It has been reported on Loch Ettrick near Thornhill.
Dumfries and Galloway Council released a statement today highlighting the toxicity of the algae to dogs and livestocks and advised against letting them, and humans, drink from contaminated sources.
A spokesman said: “This advice remains in place throughout the season as Loch Ettrick blooms fairly regularly each year.
“If you detect blue green algae, please report this to [email protected].”
Meanwhile, Dumfries and Galloway NHS have also put out an algae warning to bathers.
Speaking about the risks to swimmers and pets, public health consultant Dr Andrew Rideout said: “There are dangers around swimming in natural waters at any time, but at this time of year a key concern is the presence of blue-green algae.
“Although it’s referred to as algae, it’s actually a group of bacteria called cyanobacteria. It usually can’t get a foothold in moving water, but in areas of warmer, still water it can start to form – and it really does pose a significant risk.
“Blue-green algae emits toxins. A human or pet swimming through it with their head just above the water can be at serious risk.”
The bacteria cannot be seen by the human eye unless it clumps together. At this point, it can look like green flakes, greenish bundles or brown spots.
Dead fish can sometimes be seen in areas of water with high concentration of the toxic bacteria.
Dr Rideout listed symptoms of blue-green algae poisoning as vomiting, diarrhoea, seizures/fitting, weakness/collapse/unconsciousness, disorientation/confusion, drooling and breathing difficulties.
He added: “Anyone who does venture into natural waters should be extremely vigilant for the presence of this algae, which may not always be immediately apparent.
“Walking past waters with blue green algae should not pose a risk, but anyone who does enter these waters and starts to feel unwell should seek medical advice immediately.”
Blue green algae has also previously been spotted at Carlingwark Loch and Milton Loch near Castle Douglas and at Castle Loch in Lochmaben.