When did "turnover" occur on Boundary Waters lakes? Is it fairly consistent from year to year?

And what the heck is "turnover"?

JigNHammer

In the warmer months, warm water is at the surface of the lake. This warmer water stays at the the top of the lake and becomes warmer through out the summer. (Heat rises) There is colder water underneath this warmer layer of water. Where the two layers meet is call the thermocline.
In the fall the warmer water at the surface cools off and sinks. This process is turnover.
When turnover occurs is weather dependent

Turnover from what I understand is the lake reaching a fairly constant temperature and oxygen level from top to bottom. Turnover is also described as the churning of the lake which goes on due to the movement of the cold water from top to bottom and wind effects. Lakes which have just turned over often have a rotten eggs smell as the decomposing leaves and other organic matter is brought up to the surface from churning.