The Biblical story of Noah and the flood is not the only flood story in the world -- among others, there is the Greco-Roman story of Pyrrha and Deucalion told in Book I of Ovid's Metamorphoses -- and it may not even be the oldest. The Ancien-l email discussion group has been discussing the proposal that the Biblical flood of Noah is a reworking of a much earlier Sumerian story, from the third millennium B.C. In connection with this, one of the participants suggests a bas-relief of a shallow fishing boat could be the prototype for the ark.
For information on another flood legend pre-dating the Biblical story, see Before the Legend of Noah.
For information on another flood legend pre-dating the Biblical story, see Before the Legend of Noah.

Comments
Considering the nearly 400 ancient flood legends listed in various mythology reference books, it’s irrelevant which story predates which. The important fact is that all, or nearly all, ancient cultures shared a common knowledge of a cataclysmic deluge that killed almost everything.
A pertinent question would be: why did they all have this
knowledge?
Modern scientists are creating their own space floods now, with Martian floods appearing, in order to explain relief. Weird.