Genesis says the floodwaters prevailed for 150 days during the story of Noah's Ark.
Genesis 7:24 states that the waters prevailed upon the earth for 150 days. Genesis 8:3 repeats that the waters receded after the same period, making this a separate chronological marker from the forty days of rain described earlier.
The distinction matters because popular summaries often call the whole event “forty days and forty nights.” In Genesis, forty days describes the period of rain, while 150 days describes the period in which the waters prevailed. The full sequence also includes the later recession of the waters and Noah's eventual departure from the Ark, so neither number alone represents every day in the narrative.