What are the rules for swimming in L5R4e?

Where do I find rules for swimming/holding breath in L5R4e?

I am preparing to start a game set in the Mantis lands, and one of my players is considering playing an Order of Togashi monk. When we started talking about tattoos, I announced that anything that wasn’t defined could be created and my player asked for a tattoo that made it so the character could breathe underwater. To create a fair mechanic, as well as prepare for when a more mundane character ends up in the water, I would like to know if there is a RAW for swimming/holding breath/drowning.

I am preparing to invent something involving Stamina + Athletics(Swimming), but for now all I can find are the rules for going without food/water or sleep.