The BW and Q are great places to swim!  I've swum alone on solo trips, but in the shallows or with my PFD.  Sometimes at the end of a long, hard, hot portage I just wade in and fall into the water for relief.  After sweating that much it's not like I'm getting "wetter".
One of our regular group of campers spends almost all her free camp time exploring the shoreline from a mink's point of view.  Swimming along and checking things out on shore when they interest her.
Plusses are: clean water, few weeds, nothing in the water to worry about.  We wear shoes so we can get in/out on slippery rocks without tearing our toe nails off!  If you do swim in weeds in mid-summer you might get an itchy rash from water fleas that live in the weedy areas - but nothing that will bother you much.   :D