I've just returned to AG after a super long hiatus. The whole site's changed and unfortunately I can no longer remember the name of a game I'd played but never finished all those years ago.
The game was a bit like minecraft in that you take resources from your surroundings and build stuff. From what I remember, you're in a spaceship that crashlands into some sort of ocean, and you can use a torch/blowtorch?? - some sort of weapon to melt the rocks, fish, seaweed etc and turn them into useful materials to repair the your ship. The main character walks around in a scuba suit.
Also, I know that once you dive very deep, you come across the giant squid...or some sort of monster, I think.