For this particular piece I grabbed it off a video that my GoPro Silver took underwater. The GoPro had the standard waterproof housing it comes in. Actually I don't think there is a way to trim the input level of the onboard mic I'll have to research the GoPro's audio some more. It took some good 1080p underwater video.
Interesting sound. Did you record this when scuba diving? What mic and equipment did you use? - In fact, would be a good idea to put that in the description and tags, as I imagine that it would help people searching for this kind of sounds.