Originally posted by Cooperal:

If you can stomach the repetition you probably can because you are a Valheim player, you could just swim back by loading your character into a different world every time they get low on stamina.

You don't even have to go that far. Just log out and back on. When you log back on you have a full bar of stamina again. You lose your rested buff but you can't regain stamina while you are in water that causes you to float anyway so its not really much to give up to get your stamina bar filled up again.