CJ, my experience is accidental, when I started to fill the pond 2 small Islands popped up and their held in place by the roots from the trees I cleared out of the gully, how's that for luck.
The ground in that section of the pond was wet and boggy and the soil up here is pretty thin.
As I've mentioned before, all around the Islands are plenty of fish,insects,frogs, not to mention the occasional Herron, but I think they're after the frogs cause it drops off into 5 ft. of water.