That's an interesting question, Sharecropper. I was born in the Dallas area and remember going to a lake that was kept warm year round by some kind of plant. It left an impression on my young mind to be able play in the water almost any time of year.
As to how it affects the thermocline, if there is one, is probably dependant on where the warm water reenters the lake. If it occurs at depth, the warm water will be rising and mixing the water, probably removing the chance for anything like a stable thermocline. Where will the fish be? My answer would be: In the water! LOL
Follow Me, and I will make you fishers of men...Matt 4:19