Someone correct me, but I believe a bow works normally, there is an attack penalty for 10ft range and every 10ft beyond that.
There we go, knew it was something like that.
Ranged Attacks Underwater: Thrown weapons are ineffective underwater, even when launched from land. Attacks with other ranged weapons take a –2 penalty on attack rolls for every 5 feet of water they pass through, in addition to the normal penalties for range.
This is correct. By RAW, a bow can still fire 500 feet away underwater (if you can see that far), it just takes a -100 to the attack roll. But you might roll a 20 and get an automatic hit : )
I think most people wouldn't blame a GM for ruling that there isn't a chance that would hit, however. For my home games, I adjudicate that the range increment of ranged ranged weapons is reduced to 10 feet while underwater.
It looks like there's an underwater crossbow in the Advanced Race Guide which may be useful for what you want.