A really excellent place to dive. If you're ever in Fremantle/Perth definitely invest a day diving here. There are tons of dives (mostly by boat) on the island. The bottom is limestone covered with seaweed. This doesn't seem all that special until you go down into the caverns, tunnels and overhangs that honeycomb the reefs. These are lined with a huge variety of colorful sponges, tunicates, gorgonians and other corals. There are a few varieties of fish swimming around, but I was focused on the invertebrates. I saw more species here in a couple square feet than I saw during an entire dive on the Great Barrier Reef. We saw crayfish, port jackson sharks and a wobblegong shark as well. On the surface there was an Australian sea lion and dolphins. The dives I did were in the Bickley Bay area. Water temperature was around 19 degrees Celsius (November) and visibility was around 50 feet or so.