Thermocline fishing small lakes

[Doelman]

It's summer time and it's hot down here, water temps are in the upper 80s and will likely hit 90 before the end of the month.  I've never tried using the thermocline to locate fish, so I'm looking for some advice.  The lake is 100 acres, is very long so there is a lot of bank to fish (350' wide on average), max depth is 30 feet but 25 foot water can be found on most of the lake in the middle, the thermocline is at around 20 feet.  I've been unable to find any good structure that pokes up into or close to the thermocline, so what can I do with it to catch fish?  Should I fish the sides of the lake where the depth transitions from 22 to 18?  Should I troll with a crank at 20 feet?  Should I just forget about the thermocline? lol

[Team9nine]

I don't use the thermocline as much to "find fish" as I do to eliminate water - basically discounting anything underneath. A thermocline is just a form of "breakline," so look for where it intersects the bottom, preferably on or near structure or cover ("breaks") to locate active bass. With some other species of fish that roam more such as white bass, crappie, walleye, etc., using the thermocline as a "false bottom" can sometimes produce, especially trolling.

[A-Jay]

3 minutes ago, Team9nine said:

I don't use the thermocline as much to "find fish" as I do to eliminate water - basically discounting anything underneath. A thermocline is just a form of "breakline," so look for where it intersects the bottom, preferably on or near structure or cover ("breaks") to locate active bass. With some other species of fish that roam more such as white bass, crappie, walleye, etc., using the thermocline as a "false bottom" can sometimes produce, especially trolling.

 

Took me a while to learn how this one could equate to locating fish holding areas. 

I'm actually ashamed of myself for not getting on this a whole lot earlier - probably missed some primo opportunities. 

But once The Light Dawned on Marble Head ~ It was game changer.

Works for me right up to turnover most seasons.

A-Jay

[Turtle135]

What is the water clarity like and what is the aquatic vegetation situation? In oxygen starved situations sometimes the bass have to go shallow.

[Doelman]

The water is pretty dark green, I would say no more than 2-2.5 feet of visibility normally.  Plenty of grass on the banks, usually stops once the water hits 4-5 feet which happens in most areas just a few feet off the bank.  At least 95% of the lake is open water.

 

So I know to avoid fishing below the thermocline because of the lack of O2, so if I can't find structure that comes up to the thermocline I should bottom fish the areas of the lake where the thermocline is the same depth as the bottom itself?  I've done contour trolling for eyes up north, could contour trolling where the thermocline and bottom meet be productive with a 18'-20' diving crank?

[WRB]

There will be low DO levels below the thermocline if no current exists. Wind affects the thermocline by mixing the water column lifting or pushing down the thermal layer.

If you have a good sonar unit you can see the thermocline by the water density change, sometime a fuzzy zone a 4' to 6' thick or a darker well defined layer 1'-3' thick. 

Bass can and do go under a thermocline but it's comfortable, staying about the layer is more common.

What matters is understanding what a thermocline is and more important what depth the bait and bass are at.

Tom

[Catt]

3 hours ago, Doelman said:

I've never tried using the thermocline to locate fish, the thermocline is at around 20 feet.  

 

I've been unable to find any good structure that pokes up into or close to the thermocline, so what can I do with it to catch fish?  

 

Should I fish the sides of the lake where the depth transitions from 22 to 18?  

 

"Depth transitions "!

 

Sounds like structure to me!

 

Ya got the bank out to 20' of water that will be fishable.

 

Your saying from the bank out to 20' totally smooth?

[Doelman]

22 minutes ago, Catt said:

 

"Depth transitions "!

 

Sounds like structure to me!

 

Ya got the bank out to 20' of water that will be fishable.

 

Your saying from the bank out to 20' totally smooth?

For the most part.  They dammed up a creek in a little valley back in the 60s to make this lake so the banks are pretty steep.  I know a few sunken brush piles in the 5'-15' depth range, I just haven't found anything in that magical thermocline range.

[WRB]

There will be lots of "structure" elements that bass relate to like rocks, holders, soil transitions clay to sand, sand to gravel etc, etc., drains or gulleys that form smaller points and sharp edges, creek bends, lots of stuff including any rip rap, culverts, fence posts, stumps, the dam and all its structure. Doubt someone smoothed out the banks before filling this small lake.

If you work a jig or T-rigged worm and fan cast the entire perimeter of this lake you will discover structure elements and catch lots of bass. If you prefer to troll a deep diver to study the a depth zone select a lure the dives to 20' and troll along the bank keeping the boat between 15' to 20' and you will find what you are looking for...bass and structure. 

Tom 

Jigs 1/2 to 3/4 oz.

T-rig 3/16-1/4 oz sliding bullet.

Berkely Dreager 17.5-20.5.

Suspend bass, 3/4 oz structure spoon, chrome Kastmaster should work.

[scaleface]

Like others have stated  , eliminate water below the thermocline . . Next thing I look for is the zone where most of the fish are located . It could be right at the thermocline or shallower . Even though the thermolcline is at 15 foot , for example ,    the sonar may show most of the fish activity  at 8 foot , which was the case on a lake I went to last week . That is the depth I caught most of the fish at that day . Why the fish were at 8 foot I can only speculate . I'm guessing it was a comfort zone , perhaps the most O2 rich area of the water column .

[Scarborough817]

okay im really new to the whole thermocline business and i don't mean to hijack this thread, but just let me see if i understand this. The thermocline is basically a level in the water where below it the oxygen level is too low for the fish to be happy and it's not unlikely that they may be near this line in the warmer months because it it likely the cooler water. from what @Team9nine is saying is if the thermocline is at a certian level example being 15' then look for structure or cover around 15' and there should be some active fish there. but they may be anywhere in that 15' range.

 

Is this anywhere close to right, or am i out in left field?

[scaleface]

16 minutes ago, Scarborough817 said:

okay im really new to the whole thermocline business and i don't mean to hijack this thread, but just let me see if i understand this. The thermocline is basically a level in the water where below it the oxygen level is too low for the fish to be happy and it's not unlikely that they may be near this line in the warmer months because it it likely the cooler water. from what @Team9nine is saying is if the thermocline is at a certian level example being 15' then look for structure or cover around 15' and there should be some active fish there. but they may be anywhere in that 15' range.

 

Is this anywhere close to right, or am i out in left field?

 

Correct .  If theres a 15 foot thermocline in 100 foot of water , then you can eliminate 85 percent of the water column . The thermocline may not be the magic zone  , it can be anywhere in that 15 foot range .

[Scarborough817]

10 minutes ago, scaleface said:

 

Correct .  If theres a 15 foot thermocline in 100 foot of water , then you can eliminate 85 percent of the water column . The thermocline may not be the magic zone  , it can be anywhere in that 15 foot range .

apparently all the reading of the forums does pay off, now to just get electronics 

[WRB]

Thermocline is a transition zone or layer of water where the water temperature changes quickly several degrees within a few feet. Warmer water is lighter or less dense and floats on top of colder more dense water forming the thermocline layer. What causes the dissolved oxygen levels to drop in some lakes I'd decaying debris that floats down to the bottom, the decaying process uses up DO, the thermocline layer prevents DO from filtering deeper to replenish the lost DO in the colder deeper water near the lakes bottom.

Bass like the cooler water near the thermocline when surface water exceed 89-85 degrees, hot water doesn't hold enough DO to support the basses needs. Green aquatic plants provide shade to cool the water and most importantly produce oxygen via photothynsis during sunlight periods and shelter for prey that bass feed on. You need to consider all the ecosystem affects, not focus on any 1 thing.

Tom

[NHBull]

My lake usually turns over towards the beginning of August and creates other issues.

I suspect I will have some questions at that time

[Doelman]

From what I understand about the thermocline from my college days is that it is simply an area in the water column where the temperature rapidly changes, it has nothing to do with dissolved oxygen content in itself.  Colder water actually has higher dissolved oxygen (DO) levels compared to warmer water if all other factors are equal.  In most lakes, there's going to be a layer of detritus and other organics on the bottom that are being digested by aerobic bacteria which will be using up available DO.  When the thermocline sets up, it stratifies the water and causes the area of water above the thermocline to mix with itself and the water below the thermocline to mix with itself, but not with each other.  Because there is virtually no plant life down there, very little algae, a lot of bacteria digesting organic matter, and no air-water interface, this causes the water column below the thermocline to have very little DO.

 

I know all about the thing, I just don't know how to fish it lmao.  So it sounds like I should just avoid it all together while fishing.

[Choporoz]

https://www.bassresource.com/fishing/thermocline.html

[Team9nine]

15 minutes ago, Doelman said:

From what I understand about the thermocline from my college days is that it is simply an area in the water column where the temperature rapidly changes, it has nothing to do with dissolved oxygen content in itself.  Colder water actually has higher dissolved oxygen (DO) levels compared to warmer water if all other factors are equal.  In most lakes, there's going to be a layer of detritus and other organics on the bottom that are being digested by aerobic bacteria which will be using up available DO.  When the thermocline sets up, it stratifies the water and causes the area of water above the thermocline to mix with itself and the water below the thermocline to mix with itself, but not with each other.  Because there is virtually no plant life down there, very little algae, a lot of bacteria digesting organic matter, and no air-water interface, this causes the water column below the thermocline to have very little DO.

 

I know all about the thing, I just don't know how to fish it lmao.  So it sounds like I should just avoid it all together while fishing.

 

Pretty much nailed it. There are some lakes where there is plenty of oxygen below the thermocline to support a cold water fishery, especially in high mountain areas or in northern latitudes. These are frequently referred to as "two-story" lakes. Lakes with heavy current generation also tend to stay more mixed and may not form a thermocline. But for everywhere else, fish below the thermocline where there is minimal if any O2 are the exception.

[WRB]

If anyone wants to get into the thermal layers of water in fresh water lakes just do a Internet search on this subject. 

How the thermocline affects bass is important to understand if you fish deep structure so you wouldn't fish too deep or below the life zone. The lake I fish often has a aeration system located near the dam in very deep water, this tends to create multiple layers with good level of DO.

My point is every lake is different, some develop a well defined single thermocline while others may not develop a thermocline, some with power generation develop multiple layers similar to my lake due to deep water current movement.

For example Lake Casitas can have a 30' dense thermocline and 60' thermocline with active feeding bass near both depths all summer and bass in the grass providing a good top water bite. 

Sonar is your friend to determine what depth to target bass and so is using your eyes and common sense. Most baitfish require similar DO levels that bass need, find the bait and bass are usually nearby.

Dee Thomas likes to say shallow bass are biting bass and proved his point by flipping our deep structure lakes, we sometimes forget the basics.

Tom

[Catt]

4 hours ago, Doelman said:

For the most part.  They dammed up a creek in a little valley back in the 60s to make this lake so the banks are pretty steep.  I know a few sunken brush piles in the 5'-15' depth range, I just haven't found anything in that magical thermocline range.

 

Ya appear to have good explanations on thermocline so let's address when the bass maybe.

 

Structure does not have to be pronounced humps, ridges, cheek channels, it can be subtle changes. 

 

You mentioned grass which gives you grass lines. Are their different kinds of grass?

[Doelman]

Not sure if it's all the same type of grass, but it's all emergent stuff on the shoreline.  There's an area of submerged grass in the shallow area where the creek runs into the lake.  I don't fish in there much because it's 1.25 miles away from where I put in and solo paddling a canoe is slow business, while the lake is only 100 acres it's about 2 miles long.  Unfortunately this is the only part of the lake that has any kind of current and probably has the best summer time fishing.

 

I'm currently fishing every dock, weedline, overhang, drop off, and underwater structure I can find.

[WRB]

4 hours ago, Doelman said:

Not sure if it's all the same type of grass, but it's all emergent stuff on the shoreline.  There's an area of submerged grass in the shallow area where the creek runs into the lake.  I don't fish in there much because it's 1.25 miles away from where I put in and solo paddling a canoe is slow business, while the lake is only 100 acres it's about 2 miles long.  Unfortunately this is the only part of the lake that has any kind of current and probably has the best summer time fishing.

 

I'm currently fishing every dock, weedline, overhang, drop off, and underwater structure I can find.

Do you have a sonar unit?

Tom

[Doelman]

2 minutes ago, WRB said:

Do you have a sonar unit?

Tom

It's not a good one but yeah.

[WRB]

2 minutes ago, Doelman said:

It's not a good one but yeah.

Good enough to know what depth the thermocline is? Or good enough to know what the bottom contour and depth is and where any bait or bass might be located?

Tom

[Doelman]

It's a Humminbird 110 fishing buddy.  It'll show me the thermocline, bait, fish, depth, etc. it just has terrible bottom detail.  Unless there is something substantial on the bottom, it looks completely flat.