Unfortunately there's an easy way to win - staying at the top of the screen. Avoid sharks if they randomly spawn there but it's a clear sail to victory in a very short space of time.
It's a simple little game, I'm sure with a few more mechanics it could become a more interesting and engaging experience - if it weren't for the exploit I mentioned above it would be quite solid for what it is, maybe another danger that encourages the player to stray from the surface?