no, the river never experiences "turnover", but the lake above DOES and it has a definite affect on the temperature of the river water.
What we see is that the declining water temperature stops, and bounces up and down for a few days before, before it declines towards the yearly minimal temperature of 35 or so degrees.
I wished I had a the chart from last year, it was all very clear when the lake turnover happened...
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I think that its a bigger deal for the fishing to go from Top gates to bottom gates. Not only does that alter temperature, that also alters the currents throughout the tailwaters.
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From a practical point of view, I'd keep informed as to all changes in water conditions, if you are looking for some kind of signal that its time to start fishing for fall/winter walleye.
There's no pressure right now (and... no kidding..no bite) and when the day comes that the walleyes start to feed; it wouldn't make a lot of sense for me or others to post it for all the world to see.
Instead, do what we're doing. Keep track of conditions, persistently fish the tailwaters and anticipate the bite that's certain to come.