This morning I located the small rock garden at the western end of the run that I collided with last week. I have clearly marked the spot with a PVC post. I strongly suspect this is the same area that Pas had marked with three smaller markers some years ago. Generally, the water to the South of the mark is slightly deeper and has less small rocks.

I also removed the redundant inside Alpha marker and reused it to 'beef up' my marker on the rock garden. So please be aware that the marker that is closest to the shore at the western end is now purely a hazard warning marker.
The exact coordinates of the marker are: S -32.5676 E 115.7424