Water World is the fourth level from Alex Kidd: The Lost Stars.
This level takes place in a sunken shipwreck. Taking place underwater, the player can move in all directions to navigate the stage and avoid enemies. In the Arcade version of the game this stage features a more maze-like structure, with the player having to move between a upper and lower portion at certain times, while in the SMS version the stage is completely linear. The Arcade version also has a short above-water section at the beginning not present in the SMS version.