I took my Sony Action Cam to the pool for an underwater hockey practice this week. I shot the video in 1080P. The performance of the camera in an indoor pool is good. It is a little grainy and at times out of focus under water, but in general it is decent quality. The sound is pretty fantastic, that and the POV perspective makes you feel like you are actually underwater and playing.
I used a strap mount from the the universal head mount kit BLT-UHM1 to attach the action cam to my diving mask, making it as low profile and compact as you can get for a video setup - I am not sure how you would even do this with a GoPro with it's big square front facing form factor. I didn't notice the camera or the drag much underwater. Some people playing didn't even realize I had a camera on my head during the game until I posted the video later.