What is Thermocline?
The thermocline is a layer of the water column. In that layer, the water temperature changes rapidly and dissolved oxygen levels can be finicky due to decomposition that occurs in every body of water.
In the late spring, the water column begins to stratify, warm water on the top, and cooler water down below. The layer in between the warm water and cold water is the thermocline.
How Does Thermocline Affect Fishing?
Knowing where the thermocline is in your lake can be incredibly beneficial! As the air temperatures rise during the summer time, the thermocline layer begins to lose more and more dissolved oxygen.
This is important because the water column below the thermocline won’t have any dissolved oxygen which is needed for fish to survive. Knowing that, we can call the layer below the thermocline a “dead zone” for any fish to be caught.
Throwing a bait below the thermocline is as effective as making a cell phone call without any service…
What is Thermocline fishing?
Fishing the thermocline becomes more and more important as we get deeper into summer. The best place to find fish, is in the area right above the thermocline layer. That layer will have the most concentrated amount of dissolved oxygen mixed with the cooler water.
This layer will also thrive with baitfish, panfish, and predatory fish. Upon finding that layer, keeping your bait centralized around that depth will pay big dividends during those dog days of summer!
How to Find the Thermocline
Knowing what the thermocline is and why it is important to finding fish is one thing, but finding it can be a process. So, here is a breakdown of the best ways to find the thermocline layer with and without boat electronics.
With Boat Electronics:
A very quick way to find this layer is to locate bait fish on your graph. Most of the time, during the middle of those hot summer days, the baitfish will stage in the layer directly above the thermocline layer due to the dissolved oxygen levels and cooler water. Once you’ve located the depth of those baitfish, begin fishing channel swings, drops, humps, and banks that align with that depth. Where you find the right structure at the right depth, there will be plenty of fish to be caught!
Another great way to find the thermocline is to turn the sensitivity on your unit all the way up and go out to a deep section of your body of water. There should be a band that appears on your screen, that band is the thermocline layer. Once you have that depth, the same rules as above apply.
Above, you can see the thermocline layer is centered right around 12 foot in the water column. All of the arches above that line are fish thriving in the oxygenated water!
A final note: Lakes or river systems that have high flow rates may not form this thermocline layer. If the flow rate is high enough, the dissolved oxygen levels will remain stable throughout the water column, but there can be areas where the flow rates are not high enough on those bodies of water that will form a thermocline. Particularly, major arms that are not creek fed and don’t receive much current from the main lake.
Without Boat Electronics:
Finding the thermocline without boat electronics can be much more of a guessing game. However, there are ways to make a more educated guess. Looking at water clarity can help you decide where your thermocline layer should be located.
The more water clarity you have, the deeper that thermocline layer will be. This can be applied in almost every scenario when fishing from the bank or a vessel that does not have electronics.
If you’re fishing a murky body of water, casting your bait into the deepest portion during the summer may result in frustration. While if you have a general idea as to the average depth of the body of water and can eliminate those areas that are too deep, you will generally find success.
If you’re fishing a clear body of water, depending on depth, sometimes that thermocline layer can be as deep or deeper than 30 foot. A general rule of thumb, try to gauge how deep you are fishing by counting down your lure. A ½ ounce lure sinks at approximately a foot per second. When you find fish and can have an accurate gauge on the depth you caught them in, you can apply that to the rest of your day!