I had spent a couple of days at the Yanchep National Park and enjoyed the area and caches in the park very much.
So when I checked out what there was to do and see and which caches to find, I was amazed to find a Hippocampus at Yanchep National Park!
Unfortunately I couldn't get close to it as it is very shy but I placed a cache just off a sandy, somewhat disused track along Lake Yonderup. Maybe you can find it and post a picture if you get lucky.
ENJOY