It's all about the talking heads, trying to make them into stars in real peril, instead of just showing us Nature. I'd be quite happy if this sort of stuff was a companion programme - a Making Of, on BBC3 or straight after, or whatever. But this enforced drama is just annoying.
"Nobody can be absolutely certain what they'll find down there," says the portentous narrator. Well, maybe not absolutely certain. But I expect they've got a pretty good idea. And I'm fairly sure that the risks imposed aren't significantly greater than those on any other dive.
They're also giving science a bad name. I'm sure there's some real work going on during these expeditions too, but it's presented as, "well, we've swum around for a bit, and didn't see many fish."
Don't get me wrong. I think it's great to show the effort involved in making these programmes, too. Watching the nutters in Lost Land of the Jaguar spend two days clambering up a cliff-face gets that across. It just shouldn't get in the way of a good, solid hour of Nature.