I fish ky lake in the Danville area, crappie have been hard for me to find so far this year. I was thinking while fishing this weekend about water temp, it was about 49 degrees on the read out on my humminbird, has anyone ever checked how much the temp drops as you go down to 10 15 or 20 feet or does it level off so far down to the ground temp like the water in a well or cave?