Fishing the Fall Turnover (The Thermocline Disappears)

Big Bass caught during the fall turnover; no more thermocline and fall fishing

The fall turnover is a fear of many bass anglers.  They fear that once it happens, the fishing will be tough for several weeks.  But this is just simply not true.  Keep reading, or watch the video, to understand exactly what is the fall turnover, how the thermocline effects our fishing, and how to catch fish when it disappears. 

The Summer Thermocline 

In the summertime, most of our lakes in the South or Mid-West are going develop a thermocline.  Now your river systems won’t develop this characteristic, and neither will your lakes that act more or less like rivers. Think lakes that are on the Tennessee River or Lake Taneycomo in Missouri. The thermocline is simply the line that separates the stratification of water with different densities.  Current in rivers or lake-rivers help prevent this from occurring.  

Lake water stratifies into layers during the summer months as result of rising water temperatures.  As the Sun warms the water through longer days and higher temperatures, the water molecules near the surface increase their speed and distance from one another.  This separation of the molecules, even at the atomic level, is enough to alter the density of the water heated by the Sun.  Without going into a lot of scientific detail, warm water is less dense than the cooler water.  

On lakes or ponds, this warm less dense water is going to rest on top of the cooler more dense water.  The layers of water will not mix.  You may have noticed this phenomena  if you have tried mixing oil and water.  Oil is less dense in water, so as you pour it ends up sitting on top of the water.  Throughout the summer, this top layer of water is stirred by the wind and boat traffic.  Furthermore, the water near the surface holds aquatic plants.  These two factors help ensure oxygen is present in this layer of water.  Since the two layers of water don’t mix, the dense cool water becomes oxygen deprived as the summer progresses.  Although fish may want to live in the deepest water where it is cooler and thus less stressful, they can't because they won’t be able to breath. 

This helps make summer fishing a little easier.  On your graph you can turn up the sensitivity and see a visible line across the screen.  The line may be at 25 feet, 15 feet, or 8 feet but wherever it is, that’s the separation between the oxygenated water from the dead zone below.  This thermocline helps eliminate a lot of water since the fish aren’t going to hold any deeper than it.  All you have to do is concentrate your fishing on the structure at or above that depth and you’re going to catch fish.  

The Fall Turnover 

As the leaves begin to change color, the days become shorter with less sunlight, and the nighttime temperatures become cooler, the water temperature decreases.   As the water cools, the water density increases and at some point matches or becomes more dense than the water below.  This enables the entirety of a body of water to mix again and it does so rapidly.  The thermocline disappears and the fish are no longer limited to a specific water depth.  Anglers often remark during this turnover that the water appears slick calm and dead.  There doesn’t seem to be much life during this phase.  

Key Things to Remember During the Fall Turnover 

1) It does not take weeks or a month for the turnover to complete and the thermocline to disappear.  It can usually happen within a couple of days.  It’s not an excuse to avoid fishing during the late summer and early fall.  

 

2) The turnover doesn’t happen uniformly across the body of water.  The thermocline may set up at different depths in different parts of a lake.  On my lake, in the section that we call the main lake, the thermocline is typically established at about 16 feet.  However, we have a smaller section that is isolated and is only accessible via canal.  This smaller portion of the lake will typically have a thermocline between 10 and 12 feet deep.  I’ve found that this shallower thermocline tends to turnover a bit faster than the main lake.  The point is, if you find yourself fishing during the turnover, you may very well be able to run to a different part of the lake and continue fishing your summer patterns.  

 

3) You need to search for fish near the spots you were catching them all summer.  The reason the turnover makes it more difficult to fish, at least initially, is because the bass are no longer limited to a certain depth.  You may have been catching them on humps at the thermocline in 25 feet of water.  But when the water turns over, there isn’t anything keeping the bass from dropping down to 30 or 40 feet, especially if the bait move deeper.  

However, keep in mind that the turnover helps signal to the bass that fall is coming.  Their instincts let them know that as the water cools, the nights become longer, and the water turns over, the bait will start migrating.  They know they need to follow.  

I recommend that if your fishing during the turnover, pay particular attention to your electronics.  Don’t just pull up to a point or hump and start fishing.  Graph over your honey holes before you start fishing so that you don’t waste time on the water.  If you don’t see any fish there, scan a bit deeper to see if they have dropped.  If not, start scanning shallower structure.  You don’t need to make drastic moves.  Instead of fishing a point in 20 feet of water 200 yards from shore, move up that point to 15 feet and 150 yards for the bank.  Keep searching and start figuring out their migration patterns.  If you can successfully do that during the turnover, you’re going to be able to follow them all autumn long.  

 

4) I am going to give you a secret.  The secret is…there are no secret lures to throw during and after the water turns over.  This year, a week before the thermocline disappeared, I was catching bass on a Strike King 6XD in 15 feet of water.   Now, I am catching them on a 5XD in 10-12 feet of water, just a couple hundred yards from where I was.  So if the bass were chewing on crank baits before, they will probably still bite one now.  The same applies to your jigs, drop shots, swim baits, ned rigs, etc.  

 

It’s more important to locate the fish and choose the lure based upon how they are oriented.  If the fish have dropped to a deeper zone, or are suspended, you might want to pick a lure you can work through them.  A swim bait that you count down would be a good choice here.  If the bass are located right on the bottom, a football jig works great; same with a crank bait.  If the fish are oriented a few feet off the bottom, you might want to stroke a spoon, use a drop shot, or count down a heavy bladed jig or spinnerbait. 

Hopefully, you can use the information I have learned and apply it during late summer and early fall fishing as the water turns over and the thermocline disappears. It is not a time to avoid fishing.  The fish will still be close to where they were all summer long.  They may drop a little deeper, or they may have begun their transition.  Just take a little more time searching for them and you can load the boat. 

Tight Lines!  

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