Blue-green algae generally grow in lakes, ponds, and slow-moving streams when the water is warm and enriched with nutrients like phosphorus or nitrogen.
The algae are very small and can’t be seen with the naked eye unless they are concentrated into clumps when they can look like green flakes, greenish bundles or brown dots in the water.
When environmental conditions are just right, blue-green algae can grow very quickly in number. Most species are buoyant and will float to the surface, where they form scum layers or floating mats. Such extensive growths are sometimes referred to as blooms.
Where blue-green algal blooms develop and persist, they can adversely affect the appearance, quality and use of the water. The water may be discoloured green, blue-green or greenish brown and several species can produce musty, earthy or grassy odours.
Blooms can also cause foaming on the shoreline which is sometimes confused with sewage pollution.When blue-green algal blooms die and decay, they use up oxygen in water which can cause problems for other aquatic life including fish.
Some bloom and scum forming blue-green algae can produce toxins. These toxins can kill wild animals, farm livestock and domestic pets. They can also be harmful to human health.
Blue-green algal blooms and scums have been natural annual features of some waterbodies in Wales for many years and are likely to remain so. It is usual that, for each individual body of water affected, the frequency, duration and magnitude of blue-green algae blooms follow a predictable annual cycle. The blooms usually occur in the summer but there are no quick or easy remedies for the control of blue-green algae once they appear in a lake or pond.
Blue-green algae are capable of producing several different toxins. People may be exposed to these toxins through contact with the skin (e.g. when swimming), through inhalation (e.g. when motor boating or water skiing), or by swallowing contaminated water.
These toxins can cause skin rashes, nausea, vomiting, stomach pains, fever and headaches. Occasionally they can cause more serious illness such as liver and brain damage. Children are at greater risk than adults of developing problems because of their comparative lower body weight.
Not all blue-green algae blooms and scums are toxic but it is not possible to tell from appearance and so it’s best to assume they are harmful and take the following precautions:
Anyone who has come into contact with water containing blue-green algae should shower with fresh water immediately. Anyone who has come into contact with affected water and has become ill should obtain medical attention.
The toxins which may be produced by algae are also poisonous to animals and can cause severe illness and death. Farmers and pet owners should ensure that their animals do not have access to affected water.
In order to coordinate an effective response to algal bloom incidents in Wales and minimise any potential risks, a multi-agency approach is required involving the Environment Agency Wales, Public Health Wales and Local Authorities amongst others.
A framework outlining the roles and responsibilities of all stakeholder agencies has been established to facilitate an effective, efficient and consistent approach to the management of algae bloom incidents in Wales.