In the Noah’s Ark flood story, the floodwaters prevailed over the earth for 150 days.
Genesis 7:24 records this period after describing the rising waters that covered the mountains and destroyed life outside the Ark. The statement follows the 40 days and 40 nights of rain, so the two numbers describe different parts of the narrative rather than competing totals.
Genesis 8 then says that God remembered Noah and caused a wind to pass over the earth. The waters began to recede, and the Ark came to rest on the mountains of Ararat in the seventh month. The account continues with repeated waiting periods while Noah checks whether the land has become dry.
A common mix-up is to answer 40 days because that is the most famous flood number. In the text, 40 concerns the rain, while 150 concerns how long the waters prevailed. Some chronologies interpret the passages as overlapping descriptions, but the explicit figure for prevailing waters is 150 days.