Ahh thanks will check that sand bar out next time.
I went to the aquarium one morning and got the low down on stonefish ... basically they are like many other classic aussie animals - out to f#@$ing kill you! The guy tells me that you don't die from the toxin itself, but the pain. Within two hours you can be in so much pain that you go into cardiac arrest. .. so I kept listening... as it's not a venom, there is no anti-venom and you have to break down the toxin protein by immersing your foot (or affected region) in the hottest water possible. He reckons car radiator can be a good source if you are in a remote location. Anyway I asked about little lagoon and he said they are quite common in the inlet/creek that connects the lagoon to the ocean, but they will stay well clear of sandy or light coloured areas where they can't camoflauge themselves. Most of the shoreline of the lagoon was white shell/grit and sand so I figured it was ok.
Here's a snapshot of one of the buggers at the Oceanarium/Aquarium. Buggered if you'd see one of these amongst rocks / seaweed below choppy water!