Swordquest: Waterworld is the third game of a series of four games that Atari planned to release.  The series was to consist of Earthworld, Fireworld, Waterworld and Airworld.  Each game was to come with a comic book.  There was a contest for each individual game and there was going to be a super contest between the winners of the 4 individual games, but the final individual contest and the super contest never happened.  Earthworld and Fireworld were widely released and their contests were held.  However, Waterworld was available to Atari Club members (I don't think the Waterworld contest was ever held, but I'm not sure), but didn't make it to the stores.  This one is very difficult to find.  My theory is that anything with the name "Waterworld" is doomed to fail, so it just makes sence.  Airworld wasn't released at all.