According to Genesis, the Flood waters prevailed over the earth for 150 days after Noah entered the ark.
Genesis 7:24 states that the waters prevailed on the earth for 150 days. This figure follows the account of rising waters and comes after the separate statement that rain fell for 40 days and 40 nights. The narrative therefore uses two different time spans.
The 150-day period is associated with the waters remaining dominant before they began to recede. Genesis 8 then describes the ark coming to rest on the mountains of Ararat and the gradual decrease of the waters. The chronology continues through the drying of the ground and Noah's eventual departure.
A common mix-up is to treat 150 days as the length of the rain itself. In the biblical text, rainfall lasts 40 days and nights, while the waters prevail for 150 days. These figures belong to different phases of the Flood chronology.