From my four dives in the Great Barrier Reef (Australian National Park and World Heritage Area).
These are taken with my wife's little 8mp Canon Powershot SD1100 with a fairly nice underwater case. The flash was way to bright, and I forgot to attach the little extra thing to the case that diffuses it a bit, so most of these shots lack the real colors, and do not due the Reef justice. I don't even know where to begin with processing these, so its just bare jpeg here. Anyways, here are a few of the ones I like.
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And one of me, with a sea cucumber.