I agree with Dr Murray that these animals are surely Emydura macquarii and well out of the species natural range. This the second non-local native species (the other a Shingleback) sighted recently in this area, suggesting that these animals have been relocated/released and it looks like the turtles have established a wild population, judging by the half dozen specimens basking on the log in the photograph.
If you ever happen to get the opportunity to measure the carapace length of an aged or mature adult, it may give an indication as to which subspecies the population originates from. John Cann's book 'Australian Freshwater Turtles' published in 1998 gives detailed descriptions of all subspecies of Emydura macquarii and may be used to get an idea as to where these turtles originally came from.