Blue-Green Algae (Cyanobacteria) in Inland Waters: Assessment and Control of Risks to Public Health
2 Occurrence of blue-green algae
2.1 Blue-green algae occur in fresh-, brackish- and sea-waters throughout the world; in Scotland, they can occur in quantity in lochs, ponds, canals and reservoirs. While usually green or blue-green in colour, they may be blue, black, dark brown or red.
2.2 When present in high concentrations, colonies of blue-green algae can often be seen with the naked eye: they may resemble fine grass cuttings or take the form of small irregular clumps or pinhead-sized spheres. Blue-green algae in high concentrations in the water column form 'blooms' and, when blown on to a downwind shore, form scums which may be centimetres thick. Scums may also be seen in slow-flowing rivers and streams downstream from lochs.
2.3 Blue-green algae may also grow on the bottom of shallow water bodies and on shoreline rocks. They occasionally form thick gelatinous mats, which may be exposed as the water level falls or may detach from the bottom and reach the shoreline. These mats are usually very dark in colour (black, dark brown or green) and cohesive and are sometimes mistaken for sewage.
2.4 Some types of algae, for example filamentous algae, occasionally form surface scums and growths of some water plants, particularly duckweed, might be mistaken for blue-green algae.