Pond is fed by an Artesian well at 60 gpm. The pond is roughly 5 to 6 foot average depth and the overflow goes out to a drainage to another neighbors pond. Pond is about .10 acres. Pretty neat set up, the Artesian is masked by having it spew its water into a neat little creek he made that's about 4 feet wide and 70 feet long.
The water is 51.5 degrees at the head, 52 degrees entering the pond, and during the worst heat wave we've had, it got to 58 degrees in the shallows.
I have another neighbor, who get this, went down 4 feet and hit an artesian, the head temperature is 45 degrees! This neighbors is only 200 yards from the pond of speaking of right now and I temped both heads with the same thermometer. I never thought it was physically possible to have such cold water well temps in lower MI as 45 degrees.
Depends on the latitude of the well. Ground water temps are very close to the mean annual air temp. Mine is about 52 F. mean average air temp at my latitude. My well water with a very accurate thermometer is 51.6 F.
With all due respect if you're getting a 45 F. ground water temp in the lower peninsula, I have doubts about the accuracy of the thermometer. It's also very common for thermometers to be inaccurate.
I could see it if it's close to the surface during a colder part of year though.
Northern Peninsula Michigan and Wisconsin ground water temps are about 48 down to 45 F. the farther north and closer you get to Lake Superior. Lower Peninsula should be in the low 50's depending on latitude.
Did you know the mean average temp of Lake Superior is 39 F.? Now that's some cold freaking water!
Conversely Florida's ground water temps are over 70 F.!
