Okay, works now
First play, I thought I wouldn't need to hold space to see *anything* even in shallow water; I just went to the bottom and then exploded on invisible things.
Second play, it feels kind of aimless ... there's nothing that will cause a patient player to die once they understand to press space and pause often. Analyzing a fish takes a long time, but also isn't challenging because the fish moves at a constant rate/direction (?) and the player can pause and recharge and still catch up with it again. After analyzing ~3 fish types I seemed to stop finding new things to analyze, so just wandered aimlessly. Only died when I left it open to write this, and it ran into bombs in the background (and even then, took a while to die). Some clearer overall time pressure might help.