What your looking for is the thermocline. The coolest water will be below it, but the most oxygen will be above it. Its like when you dive into the lake, you will pass into a zone of cold water. That's the thermocline. It can vary by the day. The way to find it from a dock is by a remote thermometer. I have one of the old combo color collectors that has a thermometer on a line. I can read it from the surface. Drop it into the water, and when the temp gets a sharp decline, you have found the thermocline. I scuba dive, so when on Beaver lake in Arkansas and tenkiller lake in Ok, I've always seen the fish stacked up about a foot or so above the colder water.