I think Crytek might've screwed something up in the translation here. Now, I don't remember how it went exactly in original Crysis, but when you swim underwater, you can actually run out of respirator oxygen and start to drown after a while. The problem is, there's no oxygen meter anywhere that lets you know exactly how much you've got left. I just started swimming to get to the extraction point, thinking I'd be all sneaky and just swim along the bottom of the river to avoid all the Korean patrols, and it seemed to be working quite well until I suddenly lost all battery power and my health bar started to drain. Now, it's okay that the nanosuit runs out of oxygen after a long while, it's the fact that the game doesn't let you know how long you've got that's the problem. There's no HUD meter anywhere that I can see.