Water skinks can be very hard to identify from a single photograph. I am pretty sure this is Eulamprus tympanum - it lacks the pale mark along the dorso-lateral area from above shoulder to above forelimb that E. heatwolei has. I can see what is probably a pale front edge to the ear opening (although in my experience this character is unreliable). Subjectively I have found that E. tympanum always seems to have a rounder head profile (boof head) compared to E. heatwolei with its slightly flattened look to the head. My guess is that you saw this on the valley floor in cold air drainage basin near a swampy creek or bog.
Very good insight into subtleties of appearance, reliability of distinguishing characteristics and microhabitat preferences between these two species WillO.