My first guinea boy, loved to swim, but he first did it by accident by racing across the garden headlong into a large puddle....what a shock bless him, but he kept going back voluntarily so must have got a liking for it! Not sure if they are natural swimmers, but lots of folk do bathe them, so you could give it a go...?
One of my homegrowns (read accidental litter ) used to swim. We didn't just lob her in the bath though, it was built up over time. She liked the water, and would go up and down for ages. We put a folded towel at the shallow end for when she'd had enough.
Just be careful of the plug chain though. One of my hogs got their claw caught and gave herself a real scare.
The Resident Boars go googley eyed when they go near the bath