Locals simply refer to 'The Island' though the map refers to it as Forster Island. The unique thing is how you get there. At low tide a causeway emerges and you can walk the 100 or so meters from the mainland across to the island.
I parked my motorcycle, excited by the prospect of exploring a spot that's been right under my nose all these years. When I reached the water I could see the tide was on its way in. I gave myself half an hour, which makes little sense for someone who doesn't wear a watch but I set my mental clock and told myself not to go too far otherwise I would be in for wading and wet feet.
The island is deceptively large. There is a lovely marsh in the center is hidden from view until you are actually there. On the outer most edge there is a great view of the entire bay and smaller exposed islands a few kilometers off.
In keeping with the self-imposed time constraint I walked across the middle of the island to scout using what little time I had. Luckily I was wearing my heavy pants for the motorcycle. The brush and thorns would have shredded my shins had I only been wearing shorts.
Once on the opposite side of the island, I reluctantly returned to the little causeway. Most of it had vanished in that short time. From a distance what remained still appeared to be completely dry but when I crossed I encountered places where I was forced to step into four or five inches of water. Another ten minutes and I would have been over my boots.
I don't know the entire window of opportunity but if you cross as the tide is going out there is likely to be 3 hours before having to vacate again. The option to wade is at your discretion.
You can check my map for directions.