Parents and pet owners are being warned to keep their children and animals out of the water at a beauty spot because it is toxic.
Dorothy McHugh of the Friends of Clatto, said there had been higher than ever levels of green algae at the reservoir.
But she said that despite this she had been shocked to see not only dogs, but children in the water.
She said: “We have had green algae at the reservoir before but this year it is very extensive, worse than I have seen before.
“Usually it only covers sections of the water but this year it is much more widespread over a much larger area.”
She added: “I always keep my dog on a lead when it is around because I don’t want to take the risk of him going in when it’s like this.
“However, despite warning signs erected by the council I have seen many people allowing their dogs to go into the water. One day I was shocked to see a couple of young children, who were there with their parents, splashing around in the water at the edge.”
Dorothy said: “I would warn people to stay out of the water while it is like this.
“Hopefully if the cooler weather comes in the situation will get better but right now it has been pretty bad and people should definitely stay out of the water.”
She added: “This is a long-term issue and something that the friends group is keeping in mind.
“This is a significant blot on a beautiful area and will need to be tackled at some stage. “
Blue green algae blooms may appear as green or greenish-brown scum on the surface of water and can contain toxins that can be harmful for animals if ingested.
Symptoms include vomiting, diarrhoea, drooling, breathing difficulties and seizures.
It can cause liver damage and ultimately be fatal.
A spokesman for Dundee City Council said: “We put out warning signs earlier this year and are continuing to monitor the situation.”