Underwater Spell Casting

[Jester King]

Okay, I am in need of underwater casting in general. Where is this covered? I have found reference to Fire spells underwater needing a Spellcraft check to work so I am assuming it is possible for a mere humanoid wizard or cleric to cast underwater. Is the answer a Concentration check, with the DC 15 for violent motion? Does this assume non-aquatic humanoids can speak underwater without magical means, or is underwater casting possible only if freedom of movement, water breathing are aiding the character or the silent and still metamagic feats? Or polymorphing self into an aquatic humanoid? Your thoughts and experiences are welcomed.

[Crimson Avenger]

This actually came up in my group about four weeks ago. I believe we found the rules in the DMG. There are a couple of other considerations like line of effect and such that were really surprising. Just a quick example: line of effect is blocked at the water surface for any spell requiring an attack roll. Which means you can't cast acid arrow from surface to underwater or vice versa, but magic missle still works fine. I'd give you page # and references, but don't have my books here.

[Theolotus]

I know Stormrack has resouces for this eventuality, but I can't be sure outside of that book.