It all comes down to poop, in the most literal of senses. Even if there was just a localized flood, with animals from the immediate region, and Noah was able to wrangle ALL of those animals, and take care of each of their diets for the duration of the "flood", what did he do with the poop? Elephants, zebras, lions, monkeys, etc, etc.
I'm truly not trying to be dismissive or snarky here, but if you've ever had to care for animals, then you know you've had to clean their crap. Ever bother not picking up after a couple of dogs after just a couple of days? It's crap-tastically gross. And not properly disposing of poop will kill you- inhaling dust from mice shit can lead to lung infections that will drop you like a fly in just a couple of days.
So honestly, ask yourself, if Noah had little tiny windows up at the tippy-top of the ark, he couldn't exactly fling all of that animal crap up and out, could he? And even if he could, it would be a 24/7 job that would never be caught up with.
Oh, and then of course, there's the need to FEED all those animals to produce the poop in the firstplace. That's a boatload of hay (pun intended). Oh. And the climate control- penguins and polar bears need a different temperature to survive than a giraffe does. And I'm pretty sure there weren't air conditioners or swamp coolers around- so how was that handled? And how about making a vessel that could bear such a heavy load- with wood. Not steel. Wood. Above and beyond any standards currently in place for modern seagoing vessels, because he had A LOT to carry. But he did it, out of wood. With handmade tools. By hand. Did I mention the WOOD?
Then there's that whole thing of, if you're building an ark, how can you possibly have enough time to wrangle animals? Docile or not, how are you going to grab a passel of rhinos? How did he know what bugs to bring with him? How did he build an aviary inside the ark? The average modern zoo uses massive teams to build a series of different habitats, in SEPARATE housings. Think of the horror of the old Victorian zoos and that wouldn't even begin to be as bad as what some guy from antiquity could devise.
I'm sorry, but its not possible. Its not feasible. Its a story. Its a fable. Its a metaphor. Somebody's tent got rained out and the next thing you know.... there was a flood.
Sorry to go on like this, but the flood is one of my personal pet peeves. It just cheeses me when I think this was taught to me with a level of credence far above and beyond the stories of Greek and Roman mythology and other ancient fables. Nobody expected me to BELIEVE that a literal mouse took a thorn from the paw of a literal lion, and that they had a literal conversation with one another about it.
But the flood, oh yeah, that really happened.