While living on Maui years ago a woman brought me to a man made pool high up in the hills of Luna Lahaina to go awimming (Luna=above, Lahaina=place of the mercyless sun). It was maybe like a football field but 1/2 to 1/3 the size. It was like a built up (or above ground) swimming pool, I can't remember how high but like a small levee wall surounding it. Maybe you could call it piles of dirt where up country folks went diving. It was plenty deep enough to swim in but I don't think it really was for deep diving though.
When I think of deep diving in Hawaiian terms I think of the Hawaiians that free dive for black coral around 100' or so, give or take a bit.

Barry