The best thing about the water in Valheim is the way it can look. From a interaction point of view its more like Oil...
If you want simulation levels
1) After due preparation (IE no or low amount of Clothes) we should be able to dive.
2) Stay in the water we get COLD regardless of gear and die of that NOT lack of stamina

As it i it has some internal consistency. Loosing certain types of loot as they sink is a fair penalty in this brutal world etc Its never going to be a simulation folks but even so getting a "swimming potion" that lets you dive breath underwater maybe and generally splash a bout for much longer is worth a look maybe DEV especially if you plan to "develop" the Ocean some more as a Boss area