I had this issue, but it wasn't the one by the scuba mask, it was the one on the outside on the far right upper corner of the map. There's another item (foam?) there, but you need to do all the way to the top right to get the pass key. I went through all the locations all over to find it - ARGH!!!!
170/200 - done with this game. Next up is Alan Wake.
Also, why isn't the guide thread stickied???