Signs are up around Lakeside urging people not to touch or swim in the water.
The culprit is blue-green algae, which can be harmful to people and very dangerous for dogs.
The algae can pop up suddenly after warm weather, rain, and then warm, still conditions.
Once it appears, there is no way to get rid of it.
Eastleigh Borough Council and the Environment Agency are telling people to stay away from the algae.
Contact with it can lead to health issues like skin rashes, eye irritation, stomach troubles, and more.
If you think you’ve come into contact with the algae, it is best to see a doctor, and if your pet has, take them to a vet.
The council is closely monitoring the situation and will update the public on its website and social media pages.
