How do I create an underwater effect near lights? I'm having a pirate deputation and I want to make the room...

I'm having a pirate deputation and I want to make the room look approaching a ship wrecked boat with an beneath water effect using lights. Any thinking how I can do this (without spending the earth). Also if you have any nonspecific decor ideas I'd be bright and breezy to hear them too.
New stairway - should I varnish this previously...
Answers:    wrinkled blue cellophane over lights, maybe a small bubble blowing piece of equipment. if you can drape some blue plastic infront of a light and enjoy a small fan blow on it you can grasp some cool effects.

If you can keep the room pretty grey, set aside a a cookie tray with a sheet of tinfoil on the bottom, and shine a bright table lamp on it. the light will parallel off the foil, and any disturbances within the water (a devotee again?) will create cool reflection effects on the cieling.
Is it possible to fit a dog door...
You can dangle papir (origami) fishes on your sealings, maybe the deep sounds (delfins,whales noises). About the light, I have an idea that there are special ligths for this purpose, but its OK to buy a reguler blue or milky.