Hey Straw Hat....thanks for the scientific input. Its been a LONG time since I was in school but I have fished every fall for the last 45 years. Whether it starts to turn over, or the temperature equalizes from top to bottom, or whatever is going on, when the water temp drops below 50* is usually when I have noticed the grey dingy water, sour smell, and tough fishing for a week or two. And.....I thought it was at 39* that it stopped mixing. And that the water on the bottom would remain around 39* as the surface freezes. Otherwise, if it continued to mix, it would freeze from top to bottom at the same time......I am going to research this again.