By Dr. Hal Schramm

In Part 1 of Understanding the Thermocline, we established what happens when a body of water stratifies and how the thermocline is created. In this blog post we learn how to use this information to catch more bass in summer and fall.

In a nutshell, the thermocline is created when warm, less dense, oxygen-rich water rises in the water column while cooler, more dense, oxygen-poor water sinks. The line separating the two is the thermocline.

During summertime, anglers can identify the depth of the thermocline on electronics and eliminate all deeper water. Turn your unit’s sensitivity to a high setting and you should see a horizontal line on the screen (the thermocline). The depth of the bass fishingthermocline varies lake-to-lake. It may be as shallow as 8 feet, or as deep as 30, but it will be at the same depth throughout that body of water.

Because there’s little oxygen available below the thermocline, it’s usually void of life. But not always!

On occasion you will see bass and baitfish below the thermocline. If you see that, throw all this thermocline talk out the window and catch those fish. It’s not a common occurrence, but it does happen.

If you mark fish only above the thermocline, you can assume there’s no oxygen below it and can eliminate all that water. Fish can be at any depth above the thermocline because the temperature and oxygen are the same throughout the epilimnion (upper layer).

If you mark baitfish or bass right at the depth of the thermocline, the fish are likely finding their preferred temperature. Fish for suspended bass at the depth of the thermocline or focus on structure that intersects that depth. The fish may move up into shallow water on the structure, such as a ledge or long tapering point, to chase baitfish, but it’s a safe bet that the fish won’t move deeper.

Many lakes and impoundments stratify, but not all of them. Current prevents stratification and the establishment of a thermocline, and that includes reservoirs built for hydroelectric power generation with intermittent flow. However, a big cove not affected by flowing water may still stratify.

As temperatures drop in fall, the upper layer of water cools and the two layers mix, dropping the oxygen level throughout. This is commonly referred to as the fall turnover. It’s the sudden oxygen sag that’s likely why the bite shuts down during the turnover.  

Don’t overuse the “fall turnover” excuse, though, because the low-oxygen, funky water condition usually only lasts a few days.