Norm - My "study" here was basically a flop or failure because almost no one participated and supplied the requested temperature measurements. It was pretty hard for me to go all around to various parts of the country taking measurements in various ponds.

The warming of the pond/lake botom in summer is usually not as much of a problem as it is in winter, UNLESS you are raising cold water species of fish such as trout, whitefish, cisco and similar types. Many or most cool water fish species can with stand or tolerate a fair amount of warming depending on the species and the geographic latitude. If one has critical temperature tolerant species, the bottom temperatures should be monitored and the aerator run time should then be adjusted to obtain the upper desired threshold of temperature. We had to do this in several ponds where y.perch were dying when air temps were in the 90+F for several days straight.

If the bottom water (hypolimnion) or cool water refuge develops low or anoxic oxygen conditions then the fish cannot live there regardless of the preferred temperature. Plus with anoxic condtions overlying the benthic sediments all the invertebrate processors suffocate and their benefit is negated. So I think it is ultimately more important to have oxygen on the bottom with warmed conditions rather than have cold anoxic conditions on the bottom.

aka Pond Doctor & Dr. Perca Read Pond Boss Magazine -
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