See Norfork Lake Turn Over
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The image is created from 2005 USGS data off the Corps of Engineers website and graphed using an Excel spreadsheet. The data is collected at Norfork dam in Arkansas during the spring, summer and fall months to analyze lake stratification and turnover.
Thanks to John Kielczewski (Reservoir Control Branch of the Corps of Engineers) for his help.
The stratification of layers in the lake in the summer is evident by the temperature lines going horizontal. Once the lake turns over (a process taking several weeks usually starting in October and finishing in December), the lines go vertical as in the March or December data.
Seeing the data on a graph takes some of the mystery out of the phenomenon. It is a regular event. Once the days start to shorten in the fall and the winds increase cooling and circulation on the lake surface, the changes start to take place. The remixing of the lake's layers in the late fall usually kick off a fish feeding frenzy in the lake and also improve dissolved oxygen levels in the tailwaters where the trout live.
Data is taken from the US Army Corps of Engineers Little Rock District website. No representation is made regarding the correctness or use of this data. This is merely for illustration purposes.