It sounds like something splashing. Did something pass into your pocket of air, perhaps? Or is the pocket collapsing?
You turn around to see for yourself. You see three or four spots where water is slowly leaking in. What’s odd is that they seem very localized. Did something somehow damage the air pocket?
Maybe you should hurry up, then. You’ve got enough problems with things you barely understand as it is. You don’t need to add whatever is able to counteract divine artifacts to the list. The leak’s still fairly slow, and the shore’s not that far off… within a minute or two, you should at least be in shallow enough water that the pocket would just be keeping you from getting wet.
But just as you get ready to move again, you hear another splash. And another. You keep turning, and even look up, but you can’t see what’s causing them. You’re starting to think there’s more than one thing at work out there, though. And if they keep this up, you aren’t sure how long this air pocket will last.
They definitely seem to be getting more aggressive, so if you try to run, they might do something even more drastic. You’re going to need to come up with a plan fast.