Aquatic Spellcasting( Lords of Madness, p. 178)
Water does not impede your spells. Creatures partially or completely submerged do not gain cover or total cover when you cast a spell from outside the water. The surface does not block line of effect for any spell, including spells with the fi re descriptor. You need not make a Spellcraft check to cast a fi re spell underwater.
Partially or completely submerged creatures gain improved or total cover against attacks from land. The water surface blocks line of effect for fi re spells. Fire spells do not function underwater unless the caster succeeds on a Spellcraft check (DC 20 + spell level).