Blue-Green Algae is present in the water most of the time. It only presents a danger when there is a bloom and concentrations rise.
The green water in the photograph is the algae, not the scum or weed on the right hand side.
If the notices are displayed please keep out of the water.
Advice: (Department of Health)
People may have short term illness through swallowing or contact with the algae, including: skin rashes, eye irritation, vomiting, diarrhoea, fever, muscle and joint pain. Because they are smaller children are more at risk than adults.
In contrast to people, animals may eat or swallow large quantities of algal scum with less effect.
For further information:
Environment Agency: Tel. 0800 807060