The waters rose and covered the mountains to a depth of more than fifteen cubits. Every living thing that moved on land perished—birds, livestock, wild animals, all the creatures that swarm over the earth, and all mankind. Everything on dry land that had the breath of life in its nostrils died. Every living thing on the face of the earth was wiped out; people and animals and the creatures that move along the ground and the birds were wiped from the earth. Only Noah was left, and those with him in the ark. The waters flooded the earth for a hundred and fifty days.
The waters covered the mountains more than fifteen cubits. 'Every' living thing that moved on land perished and it lists birds, livestock, wild animals. 'all' creatures that swarm over the earth and mankind. 'Everything' on dry land that had the breath of life in its nostrilss died. 'Every' living thing on the face of the earth was wiped out. People and animals and creatures that move along the ground and the birds were wiped from the earth. The Scriptures seem to take an inordinate amount of effort to impress upon the reader that everything on the whole earth died.
Then we are told that the water flooded the earth for 150 days. Now, we've had a lot of pretty awesome floods recorded on the earth, but there's honestly no way that a local flood will flood the earth for 150 days. The standing water is going to be absorbed by the earth and run out where there are valleys between the mountains. When we accept all the descriptions of the flood, it's really very hard to understand that it could be a local flood.
But, I do understand that there are a lot of people, even among those who call themselves believers, who don't actually believe all that the Scriptures describe.