sounds like the "astronaut on a horse" problem; the ongoing challenge of getting AI to get a horse to ride an astronaut (it's always been easy the other way around). This might not be a problem anymore because AI now has lots of training data around this meme, I haven't tried in a year.

Basically there are not a whole lot of characters submerged in water for AI to train itself on. There's megatons of data of characters above water, by water, walking near water, floating on water, or swimming. It thinks you're talking about that data because it's the heaviest.