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

A map of the markers and what they represent would be useful.
It is hard to mentally picture what you mean

That does look like where Pas and Wazza had previously marked rocks. And it's certainly on the course I was on when I collided with one of them.

Agrid said..
I thought there was another rock garden marked with some poles closer toward the s-bend, or am I talking about the same spot?

Yes Agrid, you are correct. The marker for the Grumpynuts rock is roughly about where the X is, in the word 'approximate' on the picture. Or more succinctly, 'X marks the spot'.