I would strongly suggest you don't do any diving or snorkeling there or anywhere near any of the offshore islands near Eyres Peninsula. Lots of white pointer activity since the shark cage industry has ruined it for a lot of the local divers. Swim only in up to waist deep water.
Related point, for part of this trip I'll be joining a shark researcher at the Neptune Islands who is studying sharks to understand the impact that shark cage diving is having on shark behaviour.