Thermocline – What is it and what does it have to do with fishing??

[Mayfly]

If you are a fisherman you surely have heard the word thermocline but what is it? It is actually pretty simple and I will do my best to explain it to you. The thermocline is a layer or a column in a body of water that separates two other layers or columns of water from each other. There is the lower column of water which is known as the hypolimnion and the upper column of water which is called the epilimnion. The thermocline is the layer of water that is sandwiched in between these two columns of water.



Continued.....

Now you may be confused with the introduction of these two new terms, hypolimnion & epilimnion, but it paints a good picture for you as you can see in the image to the left here. You need to know these two areas to understand fully what the thermocline is. The lower layer of water is the cooler of the two. The upper layer of water is the warmer water which is warmed by the sun. The upper layer of water also contains more oxygen than the lower layer of water because this area of water is constantly getting pushed around and mixed by the wind. So not only is this upper layer of water being warmed but it is constantly being oxygenated by the wind. These two layers of water sit on top of each other except for the separation which is the thermocline. There is a point as you start to go under water that the water temp will begin to drop substantially and this is the thermocline. Once you get through the thermocline the temp will level out and then you are in that lower layer of water. See how simple that is!?    

Now you are probably wondering, what does this area (The Thermocline) have to do with fishing? The thermocline is very important but it is even more important during the hot summer months. When the surface temps rise to an uncomfortable level for fish they tend to seek deeper water that is much cooler. The problem with this deeper water is that it has been sitting down there and has not had a chance to get oxygen. The upper layer of water is constantly moving with the wind so it is oxygen rich but it may be too warm for the fish. What happens is that fish will tend to hang around and above the thermocline where they can have the best of two worlds, the cooler water and the oxygen rich water that they prefer and need for survival. This area of a lake, the thermocline, will also attract baitfish for the same reason which is very important for finding active fish.

Next time you are out on a lake that has a thermocline look for clouds of bait fish suspended in the water and you may have already located your thermocline. Some depth finders also have the capabilities of locating this invisible line in the water by adjusting your sensitivity or gain. I would refer to your manual for more information on that.

You could literally write a book on the subject but I just wanted to paint a basic picture of what a Thermocline is.

[Super Star!]

anyone who scuba dives has felt this its around 30 feet in most lakes you can hover just above it and stick your hand down and feel the cold.

[Spinach]

Great post Tim. Great information.....