I always figured the water was warmer down deep in the winter. Reason I drop shot crappie on bottom this time of year.

water temps only usually vary around 3 to 5 degrees in summer and winter. I know a guide that has studied this extensively and takes temps from the surface all the way down to 60 ft.
this is why I pay very little attention to water temps.
ive heard people say that crappie are under docks because the water is cooler,, the water is the same temp under the dock as in the sun.. water molecules mix constantly. the same with folks saying the crappie are high up on top of brushpiles in the morning because the water is cooler than the heat of the day.. this is another myth . they are higher up on top of the brush because there is not alot of sunlight penetration early in the morning,. crappie do not like bright light,.
Crappie can easily survive in most water temps. They dont go to the warmest water in the spring like many folks believe.. that is a long told myth.. they arent finding warm pockets of water deep near the bottom either in winter ,,
The crappie are where are day to day because of the location of oxygen rich water, and baitfish locations
if your interested in seeing the water temp measurements over the year , in summer, winter fall and spring, check out Bob Maindells holding the line guide services blog page.. you will have to search thru the posts but you can find very easy to read charts and graphs that show his findings. Bob is a very meticulous, organized, accurate guy and you can bet that the measurements are on point. he fishes very deep central texas lakes and was able to document a good sampling of water bodies.