Well, it was both made to be based on islands surrounded by water and just imagine how easy the game would be if Link could swim forever?

Having a really, really easy Zelda game wouldn't be Zelda at all. It needs to think your brains out and there were the boats. If Link could swim from island to island in both of the games, then he wouldn't really develop a strong relationship with the King of Red Lions and Linebeck, and they were really important characters of the game.

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