Stobsmuir Ponds have turned a vivid red colour due to a build-up of scum lying on the surface of the water.
Alan Maich, chairman of the Friends of Swannie Ponds, said he believed it was due to a chemical reaction in the water caused by bird waste and bacteria released from decomposing bread.
He said: “It happened last year as well – but much later in the year.
“Local residents have got in touch. It’s pretty unsightly.
“There’s been some comments and concerns over the swans at the pond. I was sent a picture showing one of the swans covered in the red scum. They feed in it and so it gets on them.
“Although apparently it’s not going to harm them, it doesn’t look very nice.
“It’s a combination of two things – one is the bacterial reaction while the other is an insufficient inflow of water.
“The bottom pond has a good inflow and there’s no scum on it – but I’ve been trying to get the council to turn the other on for ages. It’s not got very good pressure but it would be better than nothing.”
Maryfield councillor Lynne Short said local residents shouldn’t worry.
She added: “I know the colour is pretty vivid and the pond is looking very dramatic but so far everything suggests that it is safe.
“We genuinely don’t think at this stage that it is going to cause a safety issue for human, animal or plant life.
“I was up the other day and have taken samples for testing, so hopefully it won’t be long before we know what is turning the water red.”
She said she had also been in touch with Scottish Water to see if they could shed any light on the scarlet waters of the Swannie Ponds.
A Dundee City Council spokesman said: “We know that there is a type of algae at the pond.
“As far as the council is aware, there is no associated public health risk.
“We have advised the SSPCA of the situation.”