This is the first island inside Tuggerah Lake on the north-western side of The Entrance bridge. Much of the island is a declared Nature Reserve and off-limits to caches, but it appears to have grown since the boundary was set, with the southern end outside that boundary on land officially zoned as "Recreational Waterway".
Just around the southernmost tip of the island is a small sandy inlet where you can go ashore, and from there it's only a short walk onto the island to GZ. The water there is quite shallow, though, so it's best to attempt this around high tide.
The container is a 12cm long brown plastic tube and includes a pencil.
My thanks to lee737 who 3D-printed the containers for this series.