Do fire spells cast underwater still affect creatures vulnerable to fire?

Question

Related Question: Can magic items that deal fire damage function underwater?

As mentioned in the above question:

From the DMG p93:

Spells or spell-like effects with the fire descriptor are ineffective underwater unless the caster makes a Spellcraft check (DC 20 + spell level). If the check succeeds, the spell creates a bubble of steam instead of its usual fiery effect, but otherwise the spell works as described. A supernatural fire effect is ineffective underwater unless its description states otherwise.

For creatures that have damage reduction x/fire or regenerate damage except that done by fire, do they treat the bubble of steam the same as fire or not? eg Would a Water Troll regenerate damage from a fireball cast underwater?

Answer 1

If the check succeeds, the spell creates a bubble of steam instead of its usual fiery effect, but otherwise the spell works as described.

Sounds like fire damage to me, but you're burning them with superheated steam instead of flame.