Here are the Details of Australia.

When to go
Good All year round. Exceptional March - July.
Marine Life
Hard and soft corals and reef marine life, large pelagics, migrating whale sharks and humpback whales, many shark species including great white, turtles.
Beginners to advanced. Reef, wreck and wall diving on the Great Barrier Reef off Queensland, with day-trip dive boats from Cairns, Townsville, Port Douglas and the Whitsundays. Also liveaboards to the Great Barrier Reef and Coral Sea. Western Australia has coral reefs and gardens plus whale shark diving at Ningaloo Reef. Coral reef and mangrove diving in Northern Territory. Wreck and cavern diving off New South Wales, Victoria, Tasmania and South Australia, which also has inland sinkholes.
Great Barrier Reef, especially the Yhongala wreck and Cod Hole near Lizard Island; Exmouth, 750 miles north of Perth for whale shark diving from March to May/June; Ningaloo Reef - the world's largest fringing coral reeef - and Rowley Shoals for its pristine coral; Perth and Esperance in Western Australia; Port Lindoln and Kangaroo Island, South Australia; and Jervis Bay, New South Wales.
Moderate to Expensive
In Water
Lightweight wetsuit or Lycra suit to protect against coral in tropical seas, thicker wetsuit for southeern waters.
On Land
Shorts and T-shirts or lightweight cottons and linens year-round in the north and in summer in southern Australia. Warmer clothes for southern winters.
Box jellyfish, otherwise known as sea wasps, occur off northern Queensland and Northern Territory from November to March and can inflict severe, even fatal, stings. Venomous sea snakes abound in northern waters but though inquisitive, are rarely a danger. Crocodiles, however, are extremely dangerous. Also beare poisonous coral reef-dwellers. Sharks are common around Australia, including great whites off South Australia.
Australian Dollars