I think this game could use some more direction for the player. I spent a while swimming around different areas, killed a few sharks (once I figured out how to equip the harpoon anyway.
Adding mouse wheel to the controls at the beginning would be a good idea), and gathered some trash, but it seems the crafting system is not implemented yet.
Ultimately I could never quite figure out what I was meant to be searching for, so I repeatedly swam around and murdered sharks until I ran out of oxygen.