Blue-Green Algae

Blue-green algae are tiny organisms which occur naturally in lochs, ponds, reservoirs, rivers and in the sea. They commonly occur during periods of prolonged hot weather but sometimes occur at other times of the year. Waters which have been polluted by agricultural, domestic or industrial discharges are prone to developing blue-green algae.

In still waters the algae can multiply to such an extent that they discolour the water which then appears green, blue-green, greenish brown or dark brown. Sometimes a scum may form on the surface. This scum can appear in different places at different times, but is most commonly found at the water’s edge or shore line.

Some, but not all the blue-green algae produce toxins or release these into the water. It is not possible to tell which algae do or do not produce toxins simply by their appearance. Laboratory analysis is needed for this. Therefore, it is advisable to regard all algal scums as toxic.

The toxins of blue-green algae can cause deaths of animals which come into contact with algae, either through drinking contaminated water or swallowing quantities of scum, or shoreline matter or crust. Dogs have died after going into the water at the shores of affected lochs.

Canoeists, wind surfers and swimmers who have either swum through algal scum or swallowed it have suffered from skin rashes, eye irritation, vomiting, diarrhoea and pains in muscles and joints. Illnesses can be severe, particularly where affected water has been swallowed.

Recreational waters in Dundee are monitored by the Council. Scottish Water monitors drinking water supplies to prevent any harmful effects on health from blue-green algae.

The Council participates in the Tayside Health Board Blue-Green Algae Working Group.