Mary Sue - Sorry to disappoint you but I was not in the water itself - but at the Long Beach Aquarium looking up from underneath a large open-top open-air tank! The subject is a 6-foot shark and the lighting was noon-sun almost straight overhead! I used to both scuba-and-snorkel until I dropped a weight belt and came up too fast - that wrecked not only my sinus but any hopes of a diving career - so now I go to aquariums for my underwater shots (like the Dragonfish shot I also posted to usefilm.com yesterday)!
Hints, please. You say you took this with an E10, but you are clearly looking up at a swimming creature. How did you shoot this, through glass? What was your water depth, exposure/shutter, etc. My E10 water shots were only blue blur, very disappointing, although we were about 100 feet down, shooting through thick glass. Great silhouette!