A great flood is mentioned in the Old Testament, Greek mythology and the Epic of Gilgamesh. As with many stories like this there is a grain of truth as the people are drawing on the collective knowledge of their people. The fact is a great flood did happen in the region.
The Big Freeze or Younger Dryas ended 11,500 years ago and the polar ice sheets and glaciers began to melt. People started to inhabit and develop the area around the Black Sea. Then 8200 years ago another brief ice age occurred that lasted about 400 years. The people retreated from the area until the thaw returned 7800 years ago.
At the time there was a natural land mass which acted as a dam between the Sea of Marmara and the Black Sea. After two hundred years of melting the ocean level rose which in turn raised the level of the Sea of Marmara. The separating land mass was stressed to capacity before giving way. It flowed like a waterfall nearly 500 feet below and the salt water over took the fresh water. The water flowed for ten or eleven months and the water level raised nearly 180 feet on the Black Sea side. The resulting water way connecting the Sea of Marmara and Black Sea became the Bosporus Strait.