> why did God use this method to get rid of all the life on Earth

In the ancient world, water was the most widely recognized element of non-order (chaos). God had ordered the world to function as His temple (Genesis 1). Humankind considered themselves to be better sources of order than God (Gn. 3), and we see what happened when they had control (Gen. 4-6: sheer disaster). Since humanity had insisted on being the center of order, and since they had undeniably created quick a bit of disorder, God used the element of non-order as their mode of judgment to bring balance back to the world and to once again bring order to the world to function in a certain way (Gn. 9.1-17: there are many similarities between Genesis 1 and Gen. 9.1-17).

> I know (or I think I know) that the Holy Bible is meant to be read without taking it at the face value

It depends on the text. Some passages are very much meant to be taken at face value. Others are metaphors, similes, poetry, personification, synechdoche, hyperbole, parallelism, and many other literary devices.

Hi!
As an atheist, I started to read the Holy Bible (1910 Louis Segond’s version in French) two days ago to know what it is all about. I’m coming to the flood part and wanted to ask why did God use this method to get rid of all the life on Earth since fishes are not dying from floods. I mean, is there a reason? Do the fishes die anyway? If so, how Noe managed to save them?

I know (or I think I know) that the Holy Bible is meant to be read without taking it at the face value but I found it interesting.

Thanks in advance for your answers