So, just a couple of recomendation for your GoPro shooting when out in the water: always
1) tether your camera to your board/helmet/kite
2) use the buoy attacched to the back door (if possible)
3) use the rubber locking plug which comes with the quick release buckle.
Nothing new I guess for you all, and everything is well described in the video tutorial from GoPro.
Not following the steps above could cause loosing your camera. Trust me, I'm experienced in that.
Never, *NEVER* trust a single protection mechanism (that's why the word "redundancy"). I lost two GoPro camera in the sea, and one got soaked in salt water - and it is always been my fault. I'm so excited to get into the water that I forget to proceed through the three steps above (again, redundancy) and one protection mechanism fails. And - believe me - it happens quite often.
Please, GoPro staff, I would prefer buying original accessories/mounting systems if they would only be more reliable than they actually are:
This buckle broke on its own. No crash, just the typical bumping of the surfboard when sliding on the water. Tether leash saved my 4th gen GoPro to be lost in the sea.