Black Cat Water Temp question

[Mink Islander]

I thought that water as it cools becomes more dense until it reaches 39.4 degrees and then as it cools further, it becomes less dense -- explains why ice can form on top of water that is above freezing in temperature (usually 34/35 degrees). So why is then that the Black cat water gauge at 10 feet says 36.2 degrees while at 2 feet it is 38.8 degrees. What am I missing? Maybe it's just a calibration issue....