Michael Shea from Snails of Australia says It's either "Glyptophysa novaehollandica Family Planorbidae or Physella acuta Family Physidae an invasive from the northern hemisphere. Need a clearer image of the aperture side of the shell. If the shell is smooth it will be Physa, if it has very fine wrinkles over the surface it will be Glyptophysa". So, unfortunately I can't identify this snail, but at least we know what it is likely to be.