The sickly green slick spotted on Thursday in Wollongong’s Belmore Basin is not ocean spawn but “sea sawdust”, a type of blue-green algae.
The NSW Environment Protection Authority took samples for testing and late on Friday revealed the results: the substance is Trichodesmium erythraeum, a miscroscopic algae that relies on sunlight for energy.
It is a type of cyanobacteria – also called blue-green algae – and it is commonly called sea sawdust.
The EPA said Trichodesmium is a tropical species that grows in the Coral Sea off Queensland and is carried southward along the NSW coast by the strong southward flow of the East Australian Current.
It is not toxic but swimmers should avoid it as it can irritate the skin.