Definition of thermocline
: the region in a thermally stratified body of water which separates warmer surface water from cold deep water and in which temperature decreases rapidly with depth.
The thermocline is formed on lakes with little to no current flow that allows the mixing of the top and bottom layers of the lake waters. Since cold air and water is heavier that warm or hot air or water the heavier sinks and the warmer rises. In the following three images you can clear see the thermocline. Summer and early fall is the times that the thermocline is most prevalent with the high air temperatures this time of the year.
Why knowing where the thermocline is important to you as a fisherman? Simple it will define the maximum depth you need to be fishing. The thermocline is void of life giving oxygen so the fish you are seeking can not live in the thermocline. During the summer and early fall, adjust your unit to see the thermocline. Scan the area you are planning to fish and look for the top of the thermocline. Let’s say the top is at 27 feet as in the images in this blog. Then the maximum depth you need to fish is no deeper that 27 feet. Look for a or drop-off, shell mound or hump that is shallower than 27 feet and fish there if you see fish on them with your down image units.
Finding the thermocline is easy with the new Side Image and Down Image sonar units, in my case I use the Humminbird Onix 10 SI and the Helix 12 Gen2 Mega Scan. You will need to learn to adjust the sensitivity and contrast settings. You can find settings on this blog just do a search in the search bar. There are a lot of YouTube videos on how to tune your units.
Hope you find this blog helpful in understanding the thermocline in your fishing.