The warmest lakes

[freedivernd]

Hi Jackie, welcome to mnscuba.
I don't think there will be much noticeable difference between the lakes, but between the old mine pits and lakes there can be some difference  The cold water will be below the thermocline ~17-23' or so and the deeper you go the more compressed the wetsuit gets so the less insulation.  For the most part if you're looking to see the fish, you don't have to spend too much time below the thermocline if at all so that's good for avoiding the cold.  You might find that dipping down below the thermocline for a cool off will be in order.
Lake Superior will pretty much be downright freezing most all the time, at about 38deg. or so.

Any of the smaller, shallower lakes that aren't spring fed with too much cold water will be the warmer ones, but someone else will have to give you that list.
Fred