This is one of the most bizarre things I've seen on a bushwalk. This large, milky-blue pool is situated at the top of the exit from Dales Gorge (grid reference 681104 on the Mount Windell 1:50000 map). The only clue I have about the colour is from Bushwalking in the Pilbara by Kim Townsend, where he writes

Sometimes the water in the uppermost pools of this gorge is undrinkable due to dissolved minerals and acidity. The pool at 680108 is often a clear blue colour similar to a chlorinated swimming pool.