Little Salmon Bay
Make sure you pack your snorkeling gear for this one—due to Rottnest's warmer waters, created by the passing Leeuwin Current, there's a fascinating mix of tropical and temperate fish species in the clear waters. Aim to go at low tide and look out for bream, red-lipped morwong, zebrafish, and king wrasse, plus plenty of little colored fish. There are underwater plaques that guide you along a great snorkel trail and the waters are calm so you can enjoy flipping about. Coral reefs are about 330 feet out but worth checking out if you're a confident swimmer. Amenities: none. Best for: snorkeling; swimming.
If it's overcrowded, head to the next, bigger beach, Salmon Bay.