Not yet. Even if we solve the question of breathing underwater, our skins aren't designed to be in water too long. I suppose science may find a way to let us live underwater eventually, we certainly can't do it now.
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In normal water, no, a human is WAY too heavy. In highly salted water, we can float. There might be a place where you can float...
If they had enough air in there air tank they could be down there for a few hours but no more than that.