This game reminds me of the TMNT underwater level. :-P

It's freakin' annoying. If you go slow, you'll lose air for waiting, if you go fast, you'll lose health for colliding with enemies. You also have to be lucky to arrive at certain depths at a certain moment, 'cause otherwise the friendly creature might just be swimming out of screen.

Also, I like challenge but you should be rewarded with more air after tricky sections. I managed to get hit only ONCE while being quite deep (after the red sharks - not the pink ones) and haven't been able to reach anything that would give me enough air to go on...

Update - OK, I beat the game. It seems that there's a choke-point somewhere in the middle. After the red-shark section there were three whales I've been missing all the time because they were swimming out the screen before.

Once I got air from them the game suddenly became ridiculously easy even if the authors tried to launch hordes of near-invisible sea creatures at me... There was and abundance of air, however, unlike in the previous, supposedly easier sections...

This might need some fixing...