A dangerous algae has forced the closure of a loch – less than three weeks after it was declared safe following an earlier outbreak.

Blue-green algae (BGA) scum which formed on the loch at the James Hamilton Heritage Park in East Kilbride led South Lanarkshire Council to ban all watersports.

The algae can cause stomach upsets, skin rashes and eye problems. It is also dangerous to animals so dog walkers have been warned to keep pets out of the water.

The algae appeared in July and a family fun day had to be cancelled at the loch.

Tests proved the water was safe again and it reopened on August 13, but new blooms appeared yesterday.

The presence of blue-green algae also forced the closure of Strathclyde Loch in Strathclyde Country Park, Motherwell, and Lochend Loch at Drumpellier Country Park, Coatbridge, earlier in the summer.

Both lochs remain closed to any sports which involve being submersed in the water.

Notices have been posted next to the pond at James Hamilton Heritage Park warning that contact with the scum should be avoided.

Environmental Health Officers will continue to test the water regularly and watersports will only resume once readings return to a safe level.

South Lanarkshire Council’s recreation facilities manager Iain Walker, said: “We apologise to all our water sports enthusiasts and hope that the algae will subside quickly.”

BGA, often referred to as pond scum, is most often blue-green, but can also be blue, green, reddish-purple or brown.

It generally grows in lakes, ponds and slow-moving streams.

It floats to the surface to form scum layers or floating mats. Symptoms of contact with or ingestion of BGA infected water include abdominal pains, vomiting, diarrhoea, sore throats and blistering in the mouth.

Pneumonia and gastroenteritis, are also possible.

Ingestion of the toxic scums that can be formed by the algae is also reported to have caused deaths in cattle, sheep, dogs, birds and fish.