A health board has warned people not to enter a loch after potentially dangerous algae, which can lead to fever and vomiting, was found by environmental officers.

NHS Forth Valley said recent samples taken by Sepa at St Helen's Loch in High Bonnybridge, Stirlingshire, have indicated the presence of blue-green algae.

Some blue-green algae can produce toxins which can cause health problems such as skin rashes, eye irritations, vomiting and diarrhoea. It can also lead to fever and pains in muscles and joints, and can cause the death of livestock and dogs.

A health board spokeswoman said: "As a precautionary measure, notices have been posted next to the water body, warning that contact with the water and algal scum material should be avoided.

"Dog owners should ensure that their pets do not drink or swim in the water until further notice. Adjoining landowners and fishing interests have been advised of the situation."

The loch is not used as a public water supply, and the situation will continue to be monitored and the precautionary warning will remain in place until further notice.

Blue-green algae exist in fresh waters in Great Britain and throughout the world. They are noticed when their concentrations increase to form "blooms" and when they form scums - looking like blue-green paint - or when they collect on the shoreline.

The behaviour and build up of algae is unpredictable and can change relatively quickly, appearing one day and being dispersed by the wind within hours. It can also rapidly re-accumulate.

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