SRD:Flame Blade

A 3-foot-long, blazing beam of red-hot fire springs forth from your hand. You wield this bladelike beam as if it were a scimitar. Attacks with the flame blade are melee touch attacks. The blade deals 1d8 points of fire damage +1 point per two caster levels (maximum +10). Since the blade is immaterial, your Strength modifier does not apply to the damage. A flame blade can ignite combustible materials such as parchment, straw, dry sticks, and cloth.

The spell does not function underwater.