Unless you are shooting an ‘over/under’ and the studio flash so to illuminate the over water part, I would have thought that most of the studio flash’s light would bounce back off the surface of the water and not get through to your subject under the water, thus defeating the purpose of the light. In that case, I would have thought that you would be better of using an underwater strobe.
Ikelite do a 15 foot sync cable extension that you could use to get a strobe positioned at a distance from the camera. Perhaps you could combine more than one to get even greater distance, however, if you get more than a few metres away from your subject, the absorbtion of light by the water will be so much that you may as well not have had the strobe there in the first place. Also, I’m not sure how far the cables are capable of carrying the signal before the strobe stops responding reliably.
