Originally posted by Cap'n Bells:

Yeah i meant an additional benefit to swim skill. being "treading water" so you can stay "undrowned" and rest as the swim skill grows so does your ability to rest.. and even eventually to be able to fight whilst floating ... even get to shore if nothing in ocean eats you :-)

You can stay 'undrowned' infinitely if you have stamina. And you may replenish stamina with potions. So swimming distance is only limited by your inventory size.