Genesis says the Flood waters prevailed for 150 days in the Noah's Ark story.
Genesis 7:24 states that the waters prevailed upon the earth for 150 days. This is a distinct chronological figure from the 40 days and 40 nights during which Genesis says rain fell. The narrative uses both numbers for different stages of the Flood.
After the 150-day period, Genesis says that God remembered Noah and caused a wind to pass over the earth. The waters then began to subside, and the ark eventually rested on the mountains of Ararat.
Readers often merge the rainfall period and the total water-dominance period into one number. Genesis instead presents a longer sequence: rain, prevailing waters, recession, and the gradual emergence of the land before Noah and the animals leave the ark.