There are two types of animal for whom swimming is, at the very least, a chore:
Heavy ones (except whales).
Hairy ones.
When I say heavy, I’m talking really heavy. Old school heavy. Bare minimum, a fully grown cow. To their credit, some of these hefty beasts do give swimming a go, but they’d be severely tested by a biblical flood situation.
The best way to get your mind around the hairy category is to imagine adding a Muppet to water. Mr. Snuffleupagus would have a terrible time in the sea.
Here is a recent cartoon from the New Statesman: