This is a great, polished game, with appealing visuals and nice music.
Things that I would think about improving: The game doesn't communicate how deep you can go so you are diving and then randomly you die. It also doesn't show what you can pickup with net and what will kill you when you try to pick it up. Also the upgrade islands changing based on what you select in the map is an interesting but a little unintuitive mechanic. But all of these things can be learned by just playing and with trial and error, so it isn't really a problem, just me nitpicking a little.
Overall the game made a good impression on me, well done!