Okay, took a look at the Underwater Combat section of the DMG.
Thrown weapons are ineffective, even when thrown from outside the water. All other ranged weapons suffer a -2 penalty on attack rolls for every five feet of water they pass through.
The scrags have improved cover (+8 bonus to AC, +4 bonus on Reflex saves) from the PCs while at the surface. If completely submerged, they have total cover from the PCs. Thus, Quinn's attack would still have missed.
Fire spells ineffective underwater unless caster makes Spellcraft check (DC 20 + spell level). If the check suceeds, bubble of steam instead of fire, but the spell works as normal. The surface of the water blocks line of effect for any fire spell, even if Spellcraft check is successful.