The key word is bouyancy. Proper bouyancy and controlled breathing will be a key factor in determining how clear your pictures will be. The interiors of wrecks, wooden walls, and other building materials decay and settle to the bottom mixing with sand to create a fine silt that takes a long time to settle once stirred up. Unfortunatley the best way to get a good interior shot is to be first inside and we know that is not always possible. However, even with a moderate amount of silt in the water, proper strobe placement will still give you a very clear picture.
Photographers have a tendancy to point stobes directly at the subject.
This will cause more particulate matter to be lit in your pictures. Strobes put out an arc of light, not a shaft of light. By pointing your strobe outward or slightly away from the subject your photo will be hilighted more by the edge of the stobes arc of light and will light up less reflective matter in front of the lens. A good illustration of this can be found in Jim Church's Nikonos V Handbook. When working with wreck interiors, there are two ways two ways to show the erie feeling of the inside of these great hulks beneath the ocean.