Not being familiar with Algonquin I will assume that LT habits are consistent region to region.  That being said, I would go by water temps to find them.  Cool nights will bring the surface temps down to ~60* or so by late Sept?  So, I would guesstimate that if your surface temps are around 60* that a 12-16' crank bait would probably reach the 45-55* temps that they typically hang out in?  I don't know.  Is there a rule of thumb that can estimate the ratio of water depth to temperature that anyone is aware of?