Like many Biblical tales, "The Story Of Noah" is most probably an exaggeration of an exaggeration of an exaggeration of an event that may have happened or may not. For example, the New Testament story of the "feeding of five thousand" is an exaggeration of the earlier story of the "feeding of the four thousand" which is itself an exaggeration of the Old Testament story of the feeding of the one hundred with twenty loaves. With each telling, the number of people fed increases, the amount of initial food diminishes and the amount of food left over increases.
The flood story is no different. It is a retelling of the same basic story, with bits added on here and there and bits similarly removed. It closely parallels the story of a flood given in the Epic of Gilgamesh (an Assyrian work dating from around 2500 BC, almost 2000 years before the Biblical account was written). In fact, the Biblical account of the deluge appears to be an amalgamation of two different tellings of the Gilgamesh story. Some details are lost in the Biblical account. For example, where in Gilgamesh a raven, a dove and a swallow are sent to find dry land, in the Biblical version only a raven and a dove are sent. Both stories claim to explain the phenomenon of rainbows. It was also to be found in many Eastern libraries - fragments have been found in Turkey, Syria, Israel and Egypt. A Babylonian version of the flood story is also known - again older than the Biblical version. There is also a well known Greek version of the story.
The genesis (pun intended) of the story most probably has an element of truth within it - a series of catastrophic floods caused many deaths over a relatively short period of time. This probably happened around 12,000 years ago when a great many people were most likely displaced and/or killed due to (relatively) rapid de-glaciation as the Earth emerged from its most recent cyclical Ice Age. The story was orally transmitted through many generations and ended up being embellished to such a degree that we now "remember" it as the Biblical flood story.