The council is warning of blue-green algae in Windermere lake.
The Environment Agency, which regularly inspects lakes and rivers and carries out water sampling, has informed South Lakeland District Council that there is evidence of blue-green algae in a section of water in the lake.
Environment Agency testing has taken samples and found that the waters close to Fell Foot have been found to have a blue-green algal bloom or the potential for one to form.
Anyone using lakes, rivers and reservoirs should treat all blue-green algae blooms with caution and contact with the algae and associated algal scum should be avoided as it may result in skin rashes if the water comes into direct contact with the skin. If water is swallowed it may cause illness.
Signs have been put up at the affected bathing areas of the lake informing people about the presence of blue-green algae.
An SLDC spokesman said: “Blue-green algae can potentially make people feel quite ill if swallowed or even by just swimming in it.
“We want the public to be aware of the effects and are asking people to be extra careful and vigilant when using the lakes and rivers for recreational purposes during the summer months.
“Farmers and pet owners should also prevent livestock and animals coming into contact or drinking the affected water, as it can sometimes prove fatal for animals.
“People should observe any notices near affected areas and avoid contact or drinking water from areas identified.”
Many standing waters are vulnerable to problems with blue-green algae, typically between June and November.
All blue-green algae blooms should be assumed to be toxic and the blooms vary in colour from discoloured green, blue-green, greenish-brown, or reddish-brown. The blooms do subside and this is a temporary situation.
