MidCoast Council is urging members of the public to avoid swimming in the Manning River in the vicinity of Harrington Waters and Manning Point following the detection of blue-green algae.
Council's Environmental Health team worked swiftly once the bloom was brought to their attention on Friday, March 22 erecting signage and taking samples, with the results confirming a type of blue-green algae.
The situation will continue to be monitored but according to the Office of Water there has been a range of reports of blue-green aglae, Trichodesmium erythraeum, around the Hunter region over the past weeks.
The blooms are visible as brownish slicks in the water that can often be mistaken for oil spills. In later life stages blooms may turn pinkish-brown.
The species is not known to produce toxins however skin and eye irritation can occur following contact with the water.
Blue-green algae occurs naturally and can reproduce quickly in favourable conditions where there is still or slow-flowing water, abundant sunlight and sufficient levels of nutrients
Locals and visitors are advised they should not swim, or come in contact with the affected water - and this includes pets.
To find out more about blue-green algae phone 1800 999 457 the Algal Information Line.