Thanks for all of the additional information... If I am not mistaken the bottom of my pond does in fact "connect" to ground water, but the ground water level can also raise and lower so even if the hole originally was dug slightly into the ground water table, that doesn't mean it still is. I would assume most ponds are like mine, i.e. they are in a depression. That means the snow will naturally collect on the pond, even more so than whatever falls on the pond. Even when there hasn't been much snow, the pond was covered pretty thoroughly. I am not in a position to clear the snow off of the pond.

I think I got it regarding the supercooling.. It makes sense to me piping in air that is colder than the water would cool the water. What I am concerned about is it can go a long time here when the outside temperature is below freezing and in that time the water will ice back over. Because my pond is fairly shallow I guess I am even more concerned about the freezing and lack of oxygen. I just checked the average winter temperatures here. The average high temperature from December to February is under 30 and the average low is around 10.

Other than occaisional days when it is above 30, it seems like there would be little opportunity to pump "warm" air into the pond. I hadn't heard of the issue of ice crystals jamming up the airline. I didn't know what it was needed for, but the windmill company has a freeze protection option for a nominal cost. I don't know well the work but I hope they do the job. A part of the system is a regulator to help prevent damage if the line becomes blocked.

Thanks David for the private mail which you recapped here.

Lew