Another downside to assembled as opposed to configured body armor is that there are lot more places for water to get in. People go into shock from water this cold all the time, and all he can do is bear it out, try to refocus on up and find air again. The impact dislodged some of his inventory; his arm hurts a lot too, so he just lets that one be, drifting out at his side, where it touches something that sends another surge of adrenaline through his body. That was something, an unpleasant and moving and very large something. At least that adrenaline gets him mobile, even before he's completely got his bearings. Jason breaks the surface some long seconds after Bruce, wild-eyed from the sudden shift from feeling almost stunned to fight or flight mode. He doesn't see any sign of the now underwater again Bruce, distracted by checking what possible weapons he has left.

There's the knife, that stayed with him. A sonic device might work, sound carries well in water, but where the hell is Bruce? Jason twists in the rough waves, looking for either of them. Was that a ripple near the surface, or just another wave?

It is, in fact, an eel-like creature having an experimental snap at Bruce, which Jason can sort of see once he's been pushed underwater as well. With how dark it is, it's the movement he can see and not details. The eel thing is large enough that he can take a swipe at the tail end with his knife.