Thermocline

[GoneFishingLTN]

I was fishing a natural lake here in Iowa and seen a thermocline at 10 foot but would move across the lake or even to a new spot and see one at 12 or not see one at all. Why is this?

also some people was fishing in very deep water and that didn’t make any sense to me if the thermocline was at 10 feet

[WRB]

1st a thermocline is simply a cooler water layer transition zone about 4 degrees usually about 2’ to 4’ thick. Sometimes a thermocline looks like a thin darker line a few inches thick when the thermal layer of colder water is dense. 

2nd this is water that moves with current created by wind and can be mixed in some area and not other areas. Spring water for example breaks up a thermocline.

3rd the DO levels in cooler water can be higher the the warmer surface water fish including bass often seek the cooler higher oxygenated water in and below the thermocline, it’s not a dead zone. The thought a thermocline is like a sealed sheet of water preventing the fish moving deeper isn’t factual.

Tom 

[PressuredFishing]

2 hours ago, GoneFishingLTN said:

I was fishing a natural lake here in Iowa and seen a thermocline at 10 foot but would move across the lake or even to a new spot and see one at 12 or not see one at all. Why is this?

also some people was fishing in very deep water and that didn’t make any sense to me if the thermocline was at 10 feet

Bass love cooler water right, what ive learned is the thermocline doesnt always mean bass are above it, its actually cooler water so they will go under it, but usually not by a ton. as for the thermocline moving current can oxygenation of water can break it up, for instance if a lake pulls water from a d**n it creatures current, or if there is wind on the surface, it creates current, expecially now in fall, (not where i live but maybe for you) with the cooler temperatures and wind moving that thermocline may be starting to dissolve.  never overlook the thermocline, because bass love cooler water and have caught them sitting right above and in the thermocline, sometimes even below it.

[jimmyjoe]

   Thermoclines are the hardest thing for me to understand about fishing. I used to fish the rivers, which do not develop thermoclines.

   If you're in Iowa, you can read the DNR fishing letter that comes out every Thursday. This summer, it has constantly had lake thermocline levels in it, cautioning the fisherman to not fish below that level because, " .... there is no oxygen below that level, and the fisherman would be wasting their time." Some of these levels have been as high as 7 feet of depth.

   Yet people have caught good fish well below that.

   As much as I respect the DNR knowledge base, I think they're wrong on this.

   In fact, I think most people are wrong on thermoclines. I see them as a phenomenon that isn't well understood at all. 1.) I think their severity is different in different lakes. 2.) I think this low-oxygenation factor can vary so much that only a D.O. meter could give you a reasonable assessment .... and then a storm could change everything the next day. 3.) Even if the low-oxygen characteristic is true, I think it may have less effect of the fish than people think.

   A powerful thermocline would depend on powerful water stratification. I (personally) doubt that stratification is that powerful and stable if there is fairly constant wind.

   I think we're scared of the bogeyman. I see too many things that contradict conventional wisdom.

 

   As usual, though, I could be wrong.        jj

 

  

  

[scaleface]

2 hours ago, jimmyjoe said:

   Thermoclines are the hardest thing for me to understand about fishing. I used to fish the rivers, which do not develop thermoclines.

   If you're in Iowa, you can read the DNR fishing letter that comes out every Thursday. This summer, it has constantly had lake thermocline levels in it, cautioning the fisherman to not fish below that level because, " .... there is no oxygen below that level, and the fisherman would be wasting their time." Some of these levels have been as high as 7 feet of depth.

   Yet people have caught good fish well below that.

   As much as I respect the DNR knowledge base, I think they're wrong on this.

   In fact, I think most people are wrong on thermoclines. I see them as a phenomenon that isn't well understood at all. 1.) I think their severity is different in different lakes. 2.) I think this low-oxygenation factor can vary so much that only a D.O. meter could give you a reasonable assessment .... and then a storm could change everything the next day. 3.) Even if the low-oxygen characteristic is true, I think it may have less effect of the fish than people think.

   A powerful thermocline would depend on powerful water stratification. I (personally) doubt that stratification is that powerful and stable if there is fairly constant wind.

   I think we're scared of the bogeyman. I see too many things that contradict conventional wisdom.

 

   As usual, though, I could be wrong.        jj

 

  

  

Bass Pro Shop use to sell a temperature / light meter . It was a probe that was lowered in the water with a hand held display that would give a readout . I only used it on my home lake . The light and temp would gradually decline until it reached the thermocline ,then  they would both plummet . That was a handy little device and inexpensive . I left the batteries in and they leaked out ruining it .

[Tennessee Boy]

16 minutes ago, scaleface said:

Bass Pro Shop use to sell a temperature / light meter . It was a probe that was lowered in the water with a hand held display that would give a readout . I only used it on my home lake . The light and temp would gradually decline until it reached the thermocline ,then  they would both plummet . That was a handy little device and inexpensive . I left the batteries in and they leaked out ruining it .

Yeah I had one of those and used it a lot.  I don’t understand why no one makes anything  like it anymore.  

[WRB]

Today’s sonar clearly displays a thermocline, no lowering a probe needed.

Back in the 60’s I had a temperature probe on 50’ reel of wire to lower into the water to find a thermocline. I also put the probe into the basses throat to measure body temps to determine the water temps the bass was acclimate in. This helped me to know where to fish and how deep. The flashers we used didn’t display a thermocline, not enough power.

most lakes develop 3 thermo layers. Thermocline is located between  the top 2. 

Bass prefer water about 70 to 80  degrees and seek that zone for comfort if available. Cold water species like trout prefer colder water around 50-60 degrees with good DO and that maybe very deep in the warm water periods. 

The dead zone is deep water where decaying debris is using up DO do to lack of current. This does occurs in some ponds and lakes without bottom layer current and the reason aeration systems are added.

Tom

[scaleface]

34 minutes ago, WRB said:

Today’s sonar clearly displays a thermocline, no lowering a probe needed.

Yes , I could see the thermocline on my depth finder . The probe told me what was going on down there with both light and temperature . After awhile I quit using the probe because I knew  what it was going to read . I still used it when the thermocline was absent .

[Chris Catignani]

4 hours ago, jimmyjoe said:

   Thermoclines are the hardest thing for me to understand about fishing. I used to fish the rivers, which do not develop thermoclines.

   If you're in Iowa, you can read the DNR fishing letter that comes out every Thursday. This summer, it has constantly had lake thermocline levels in it, cautioning the fisherman to not fish below that level because, " .... there is no oxygen below that level, and the fisherman would be wasting their time." Some of these levels have been as high as 7 feet of depth.

   Yet people have caught good fish well below that.

   As much as I respect the DNR knowledge base, I think they're wrong on this.

   In fact, I think most people are wrong on thermoclines. I see them as a phenomenon that isn't well understood at all. 1.) I think their severity is different in different lakes. 2.) I think this low-oxygenation factor can vary so much that only a D.O. meter could give you a reasonable assessment .... and then a storm could change everything the next day. 3.) Even if the low-oxygen characteristic is true, I think it may have less effect of the fish than people think.

   A powerful thermocline would depend on powerful water stratification. I (personally) doubt that stratification is that powerful and stable if there is fairly constant wind.

   I think we're scared of the bogeyman. I see too many things that contradict conventional wisdom.

 

   As usual, though, I could be wrong.        jj

 

  

  

Your spot on about the bogeyman. One thing that important to know about a thermocline is what makes it tick. As water gets cooler...it becomes molecularly denser..ie heaver. In the winter...as the upper layer get colder...it will transition to the bottom...thus the lake turnover and there will be no thermocline. As the lake warms back up in the spring/summer...the thermocline will form again. Some really deep lakes will actually have two theromclines. Once a thermocline forms...its still oxygenated...but it slowly starts to deplete.

There are many ways in which oxygen can enter the water under the thermocline. A cold rain for example will sink if the water is cooler than the surface water. An under water spring. Creeks and river currents...just to name a few.

[jimmyjoe]

41 minutes ago, Chris Catignani said:

A cold rain for example will sink if the water is cooler than the surface water

 

Yeah ..... that's what I meant about a storm changing D.O. levels overnight. New water introduced plus (possibly) violent wind, and you've got a whole new ballgame.             jj