I don't know much about Coopers Creek, but the yabbies, Murray crays, turtles etc do this in NSW along the Darling and in tributaries of the Murrumbidgee in the riverina when there is a black water event. The water becomes de-oxygenated when a heap of organic matter (read sheep poo) is washed in from rain and starts to decompose. They leave the water and sit at the edge.
Regards
JAs