Actually, there is a lot of evidence that the Big Flood did, indeed happen. Additionally, I have been told that there are many flood stories, not just the one in Genesis.
Even more, there is a difference between a myth and a lie. You may believe that Genesis is a lie, but it does not come close to meeting the literary criteria of a myth.
No. There is plenty of evidence of floods throughout history. There is no evidence of a global deluge. And of course there are many stories of mythological floods. Moses allegedly wrote the Pentateuch, but however was responsible simply lifted the Mesopotamian tale of Gilgamesh and altered it to suit his purposes. As serious a case of copyright infringement and plagiarism as any in history.