After take off it looks like the pilot planned to stay to the left of Cowan Creek to facilitate a turn back towards Cottage Point. Why, to shorten his track miles back to Long Reef and Rose Bay climbing out down Coal and Candle Creek and or to allow the front seat passenger with the camera to take some overhead photos of Cottage Point the place they just had a very nice lunch.
In the turn the pilot miss identified Jerusalem Bay for the main river. Even after spending a lot of time in the area this is still possible to do, as at low level the forks in the river at different spots can look similar. The very experienced pilot has then found himself in the middle of a boxed bay somewhat heavy at low level with a 10 to 15 knot tail wind and simply stalled in the turn with no chance of recovery.
A fact the ATSB has not mentioned is that this very experienced and comportant pilot
had an unfortunate and serious landing accident at Rose Bay in the company C-208 just a few days before the accident in question. (Four months to repair) Why mention this, maybe it was playing on his mind at the time rather than the job in hand.
We will most likely never know.