I think they use the dx7 mode, which has no water reflection.
I don't know about this, but as part-time xbow I can say, that the bubbles are a pretty nice and accurate target if you've got at least a bit of an idea how deep the water is. Since you are slow down there and can't swim in different highs. So, don't try to evade archers by swimming.
But another thing - how about implementing drowning and arrows not beeing able to break the water surface (or some kind of that, since the water would acctually slow down the arrow pretty much).