I think Australia has the highest number of deadly snakes in the world, prolific great white sharks in the south and a shed load of spiders that can kill by looking at you from 20 feet that live in dive gear, theres invisible jelly fish that can kill in the north and blue ringed octopi in the middle that cause total body paralysis - and heaps of other things

Wrecks - scattered mostly down the east coast - some in the west

Brisbane is hot and shitty, Melbourne is well Melbourne - So your best bet is Sydney - a few good Rebreather friendly shops here too.

S