In Genesis, the floodwaters prevailed over the Earth for 150 days after Noah’s Ark was afloat.
Genesis 7:24 states that the waters prevailed for 150 days. This is a separate measure from the 40 days and 40 nights of rain. The rain describes the period of falling water, while the 150-day figure describes how long the floodwaters remained dominant.
Genesis 8 then begins the process of recession: God causes a wind to pass over the Earth, and the waters gradually abate. The Ark eventually comes to rest, and Noah later tests the condition of the land by sending out birds.
Readers often combine the story’s several numbers into a single flood duration. Genesis instead gives a sequence of intervals, including the rainfall, the prevailing waters, and the later waiting period before Noah leaves the Ark.