Q u o t e: Yes, in most cases if you are roaming around the wilderness swimming is a bad idea. Even if you don't have any armor and weapons with you, you still have to carry a lot of equipment with you. And it is nearly impossible to cross a fast flowing river OR a steady lake with a backpack. Even if you manage to do it, afterwards you and all your food and spareclothing is wet. Then you need to light a fire. Then the monsters will see it and come killing you. And you don't have any weapons remember?.
And don't forget the amazonian %@@*#/#!@#%% fishs (Vandellia cirrhosa and Tridensimilis brevis)! They are parasites that swim into your sexual organs and feed on you from the inside. Do we really want to risk having our sexual organs amputated when we swim in the streams in jungle-kurast?
/edit: omg, "pen.is" and "vag.ina" are bad words? Seriously Blizzard, you can't be THAT american! It's a medical term, ffs.