Okay, it's not an island surrounded by water - it's a different kind of "urban" island. No need to set feet on the island itself, or in any of the landscaping. And ... contrary to what you might be thinking, it's not a nano. I've never hidden a nano, and I don't plan to start now. Muggle presence may be high at times, so be sneaky when you make the find.
Probably not the best idea to park along the side of the road at this busy spot. There is ample parking nearby ... in Mitchell Park, or in the church parking lot.