Costume to swim in?

Hmm.  My water aerobics class has announced they want to "dress up" for Halloween as we have a class that morning - of course, I must presume this essentially means "dress up their heads" as the rest of the body has to be submerged in chlorinated water for the duration...

I can't think of anything sufficiently waterproof at the moment - maybe a gaudy necklace and earrings with something made of bits of craft foam for my hair?  Uh... ??  Er...? 

Ever run into anything like this? Ideas? Help!