Pimp My Light, Submariner Version
UPDATE #2: We have a winner. Check out this fantastic, DIY PVC housing before trusting your baby to zip-lock bags.
Strobist reader Maneeacc has more guts than I do, sticking an SB-800 underwater to light from below sea level.
Actually, I have done this before. But I would use an S-26 for this task, as it is about $200 less gutsy.
He is using three zip-lock bags to stave off the $320.00 water for long enough to make his photos. I would suggest a mod that will offer more protection for his flash, while giving him better light. First of all, I'd wrap the flash in two layers of (neutral colored) condoms, as they offer form-fitting water protection.
Use the largest sized condom you can find, to avoid overstretching. Which means you get to go into the drugstore and ask, with a perfectly straight face, for the absolute largest sized condoms they sell.
Be sure to use a spacer of some kind if you are gonna shoot at high power levels, so as not to cook the condom to your flash head. Which would be kinda hard to explain to your camera repair tech.
But further, I would suggest putting the flash, slaved, in a decent-sized, frosted white tightly sealed tupperware container. Stick the appropriate amount of weight in there for neutral buoyancy and you are good to go with a safer, softer light source.
That said, if you are gonna go sticking your flashes underwater, you are totally on your own. Test, test, test.
And if you do not have an optical slave, this is one area where Gadget Infinity radios trump Pocket Wizards, for hundred$ of reasons.
(Cool shots, Nafis.)