I went out and took temps today.
Surface (6" down) - 91�
3' - 86�
5' - 82.3
10' - 79.7�
12' - 70�
13' - 69�
15' (bottom) - 67�
This is the first time that I was able to take depth meanurements without ice on the water, and I either couldn't find the deepest spot, or it filled in more than I thought. The pond has dropped 14" from it's highest level this Spring, and even that level was about 4" from going out the overflow pipe.
91 F. for surface temp! Wow! It must be because you aren't running your diffuser lately as we are at about the same latitude and you have much more wood cover near your pond than I do.
