Noah's Ark - truth, half-truth, or flat-out myth?

The genetics issue is the same as the genetics issue with Adam and Eve. People ask, "How could people have multiplied, since Adam and Eve's descendants would have had to breed with each other, and their genes would create messed-up people because of the gene pool." Same issue with the animals. At that time, the gene pool was fairly unmarred because sin had only just entered the world a short time ago, and there wasn't enough time for the gene pool to deteriorate. It deteriorated after a long period of time. So the animals wouldn't have been sick and weakly because they were mating with their relatives, and neither would people.

As for the water problem. It says in Genesis 1:6-7, "And God said, "Let there be an expanse between the waters to separate water from water." So God made the expanse and separated the water under the expanse from the water above it. And it was so." There was water under the sky - the sea - and there was water above the sky as well. Genesis 7:11 says, "In the six hundredth year of Noah's life, on the seventeenth day of the second month—on that day all the springs of the great deep burst forth, and the floodgates of the heavens were opened." Water rose from the seas, but water also came from the sky, since there was water above the sky. Now there isn't because it was used up in the Flood.