The council is issuing a warning on behalf of the Environment Agency, as blue green algae has been confirmed present in some waters in Alexandra Park.
The Environment Agency has confirmed the water at Shornden reservoir and the stream below it that runs to Harmers reservoir have high levels of the algae.
These algae can produce a scum that is toxic to animals and can harm people.
Hastings Borough Council is warning people and their pets to stay out of the water and is putting up signage around the affected areas to warn members of public.
It has also warned the fishing club and they are closing off access to Harmers reservoir.
Access to Harmers wildlife pond and Shornden reservoir is already restricted.
This natural phenomenon will go away in time when temperatures drop significantly but this is likely to be later in the year.
Algae occur naturally in inland waters such as rivers, streams and lakes.
When conditions are ideal for growth, an algal bloom can occur. During a bloom, the water becomes less clear and may look green, blue-green or greenish-brown.
Scums can form during calm weather when several bloom forming species rise to the surface. This can look like paint, mousse or small clumps.
Cyanobacteria or ‘blue-green algae’, a type of blooming algae, can produce toxins. These toxins can kill wild animals, livestock and pets.
They can also harm people, producing rashes after skin contact and illnesses if swallowed.
Algal blooms block sunlight from reaching other plants in the water.
They also use up oxygen in the water at night which can suffocate fish and other creatures. Oxygen is also used up when the bloom decays.
Any other reports of suspected blue green algae should be made to the Environment Agency on 0800 80 70 60.
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