I would probably try to keep from staying at a known nuissance bear campsite.  The south shore of South Arm Knife has been a bear feeder for at least a decade, most likely because it's an easy day's paddle from Moose Lake and people aren't vigilant about their food/trash.  Take an island campsite, or be ready to pack up and leave.  Sure, bears can swim, but my experience is that they typically don't hole up on an island when there's lots of food on the mainland.  At least Knife Lake has lots of campsites, so if you have to pack up, you can do it without having to portage.

I would definitely stay away from a known problem bear on a hard to reach lake with only 1 or 2 campsites.