Snorkelling at the "Fish Aquarium" in the Ahihi-Kinau Natural Area Preserve, before it was closed for regeneration in August 2008. It was planned to be closed for two years. That closure has now been extended until July 31, 2012. Here is a link to more info about the area.
A write-up of our experience on this trip is contained on the following thread from the Canreef Aquatics bulletin board.