I recently visited the Bungala River estuary at Normanville where I was able to take several photos, which I have posted to iNaturalist.
Those photos show various views of the smelly, dirty green, brown and light grey scum on the damp sand, and shallow pools (also on the surface of the lower estuary’s main lake, very brackish and subject to inundation on high tides, including very recently).
My iNaturalist post suggests that my photos show Karenia mikimotoi. Obviously, I am only guessing when I suggest Dinoflagellate aetiology, because I am not aware of any laboratory sample results from this location, if any sampling has occurred recently (in the setting of the catastrophic toxic algal blooms affecting the area currently).
Karenia mikimotoi is a member of the Dinoflagellates Superclass, Dinoflagellata.
This is the most likely organism implicated, based on the data obtained from PIRSA/SARDI and other expert research bodies, pertaining to the more highly publicised sample testing of water from adjacent parts of coastal Fleurieu Peninsula, and bearing in mind that the entire Fleurieu coastal waters are affected by this very extensive bloom.
Another observer posted their photos from Encounter Bay on iNaturalist.