Small flatworm, length only 10-15mm as pictured. Found under a log about 2 or 3 metres from the creek in an area clearly affected by recent flooding (4 weeks ago).
The species was originally described from specimens collected from a patch of grass (hence species name graminicola - grass dweller) in an urban garden in Petersham, Sydney. It was also later found in a garden in Carlingford, subsequently found near Camden in a remnant of the Nepean scrub, and more recently it was recorded near Slatey Creek, Holmesville, NSW. I suspect that the species is native, and possibly prefers riparian habitats.