As of May 09, 2006 I have uniform water temps throughout my water column of 59.5 degrees F. I am located in southeast Nebraska. If my aerators only kicked on below 58 degrees there would be long, long periods of time between aeration events during the summer. During this time there would be a buildup of bad gasses and anoxia in the hypolimnion that would be released during aeration and probably result in a net loss of dissolved oxygen. I would be inclined to look at options that would add oxygen to the well water and distribute to the hypolimnion directly. Then I would buy a surface agitator from a company such as Kasco to aerate epilimnionic waters. This would allow the thermocline to stay put, but keep all areas of the pond habitable to salmonids. According to Cecil's previous post (IIRC), salmonids will often die of anoxia before they die from warm water stress. Aquatic ecosystems may have a device that would measure DO at the thermocline and kick on your surface agitator if your DO drops below 6 ppm. All of this is based on your lack of available water volume. I can dump 40-50 gpm of 54 degree water in my ponds in the summer and I'm not even certain I can keep yellow perch alive in my .15 acre pond. This could be looked upon as a "available well water (cooling) to pond water volume ratio". Cecil's is even better than mine and it allows him to overwhelm the summertime solar heating effect that will kill your trout. If this ratio is low you may be tip-toeing a windy ledge.

Holding a redear sunfish is like running with scissors.