Finding the Thermocline

[Grumpy]

In a post about Rough River, the poster was told to find the Thermocline but he replied that his fish finder was old and didn't show the thermolcline. It is really not necessary to find the actual Thermocline or its real depth, all you(we) really need to know is the DEPTH OF THE LAKE BELOW WHICH THERE IS LITTLE OR NO OXYGEN.


Fish, like people, need oxygen to live and they will not stay in a part of the lake that has little or no oxygen. They will always stay at or above the level (depth) that holds as least 2 parts of Dissolve Oxygen. At least that is my figure but I have read that they must have 3 parts and even 4 parts Dissolved Oxygen to stay in an area.

In the Summer time, before I go fishing on any local lake I always check the Louisville Corps of Engineer site for that lake and get their reading of LAKE TEMPERATURES. In case you don't have it, here is the link to the COE site: http://www.lrl.usace.army.mil/wc/reports/lkreport.html

Click on that link and you will get the Louisville District Daily Lake Reports. Go down the left side and click on the BLUE name of the lake you want to fish, e.g. Rough River Lake. That will get you to the COE page for that lake, go down towards the middle and you will see a line that says: LAKE LEVELS and LAKE TEMPERATURES, click on LAKE TEMPERATURES and you will get a page with a lot of graphs but to get an better and easier listing click on the line at the top that says CLICK HERE TO SEE RAW DATA . . . . That will take you to a page that says WATER QUALITY DATA FOR ROUGH RIVER LAKE. Below that will be a listing of depths showing the temperatures and disolved oxygen level for each depth.

The most current listing is 07/09/2012, which for my purpose is good enough since it has been hot and relatively dry since then. I look down the list and find that below 19 feet there is less than 3 parts oxygen and so when I go fishing I figure that fish are above 19 feet and I fish above that depth and don't fish anything deeper than 19 feet. Now, these readings are taken at or close to the dam but I figure that in other parts of the lake, the fish will be at or above 19 feet also.

I hope this helps you to find fish and not have to fool with your depth finder all the time.

Grumpy

[peter]

Do you know if similiar info is available for corps Nashville District?

This is very good info to know. Must follow directions exactly in post to get to the easy to understand temperature and oxygen readings at various depths.

Thanks

[Grumpy]

Peter, you are welcome. I haven't ever found where Nashvile COE provides this data but then again I haven't looked lately.

POST SCRIPT: You (we) can also find out when the FALL TURNOVER has occured by usding the same COE site and data. I have found that once the Thermolcline sets up in late Spring or early Summer, the COE data will be pretty clear for the depths that have little or no oxygen and within a couple of feet it will remain the same until after the Fall Turnover. Using the Rough River site again, at 20 and below there is 2.0 or less oxyben all the way to the bottom. At the surface its 6.1 and at 50 feet its 0.1. They only provide this every couple of weeks but it will be pretty much the same until after the Turnover.

Depending on when they take the readings, after the Fall Turnover, the Oxygen level will only drop off slightly from top to bottom, e.g last year in late October. it was 5.1 at the surface; 4.6 at 10 feet; 4.5 at 20 feet; 4.4 at 30 feet; 4.4 at 40 feet; and 4.3 at 50 feet. BTW, the water temperature was 62.2 at the surface and 63.11 at 50 feet, there there was no longer any strata in the lake and the Turnover was complete.

GRumpy

[fishinfreak]

Thanks for the thread this will help everyone out tremendously.

[peter]

Thanks for the thread this will help everyone out tremendously.

Yeah. To know where the fish will not be is huge. Helps my confidence a lot.

[Tom523]

I use the same data but look for the first biggest change in temperature. On 7/16/2012 Barren River Lake readings are:

Depth Temp Oxygen
0 82.9F° (28.3C°) 8.6
5 82.9F° (28.3C°) 8.6
10 82.9F° (28.3C°) 8.0
15 81.5F° (27.5C°) 4.7
16 81.0F° (27.2C°) 3.1
17 79.5F° (26.4C°) 0.2
18 78.4F° (25.8C°) 0.1
19 77.9F° (25.5C°) 0.1
20 74.8F° (23.8C°) 0.0
21 74.3F° (23.5C°) 0.0
22 72.3F° (22.4C°) 0.0

The first larget gap is between 16 and 17 ft. . The largest gap in temperature tells me where the thermocline is. This has worked for me for years on Rough, Barren, Green, Nolin, and Cumberland. This is where I'll choose cover in that depth to set my bobbers for crappie or troll.

[Grumpy]

Tom, you are absolutley right. I didn't want to get into that in my original post but I also check the change in temperatures to get the probable location of the thermocline. HOWEVER, over the years I have been doing this, I have found that it is much easier to see the drop in oxygen content then the drop in temprature. Both ways are correct and will help to eliminate a lot of unproductive water by not fishing deeper than thermocline/depleted oxygen depts. As Peter said, "To know where fish will not be is huge."

Grumpy

[Todd2]

Looking at the charts, for Taylorsville on 7/15, it looks like the thermocline was around 11 - 12 feet. I marked fish deeper than that and even caught a few deeper this past weekend, any thoughts on why they would drop below that level?

[Grumpy]

Todd, sorry if I made it sound lake there is ABSOLUTELY POSITIVELY FOR SURE no possibility of any fish being below the Thermocline/depleted oxyben depth, there may be some fish inside the Thermocline and even below it AT TIMES. However, from everything I have read, they will not stay long in areas where there is little or no oxygen and that is why I always fish at or above the Thermocline (when there is a Thermocline). As Buck Perry said in his SPOONPLUGGING book, all of the fish will be in the same ten percent of the water and eliminating areas where the fish are not likely to bi is the most important part of finding fish (or words to the effect).

Click on the link below for a good article on the Thermolcine and lake turnover.

http://kentuckyoutdoorsmagazine.com/blog/?p=203

Grumpy

[Todd2]

Todd, sorry if I made it sound lake there is ABSOLUTELY POSITIVELY FOR SURE no possibility of any fish being below the Thermocline/depleted oxyben depth, there may be some fish inside the Thermocline and even below it AT TIMES. H

Click on the link below for a good article on the Thermolcine and lake turnover.

http://kentuckyoutdoorsmagazine.com/blog/?p=203

Grumpy

Got it.. thanks for link, some good stuff in there.

[airnet]

I find it easier to locate the thermocline by turning your sensitivity up on your fishfinder/graph ,,,,it usually will show a gray line running diagonally across your screen,,,,and most of the time thats where you will see the fish are located on your screen as well,,,,

[Grumpy]

Airnet, you are right about ONE WAY to find the thermocline but apparently you didn't really read my first post in this thread. I was trying to help out a fellow that said his fishfinder was old and did not show the thermocline. By going to the COE site for a particular lake, before you go fishing, you can get a good idea where the thermoline is without having to fool with the electronics. You are also right about fish bunching up at and just above the thermocline. The last article I cited says that also:

"In a stratified lake, fish will typically not venture very far below the thermocline, except for brief forays in search of food or other meanderings. They will, however, often hold right at or just above the thermocline. This is why knowing whether or not a lake develops a thermocline and if so, at what depth, is so vitally important to fishing. If an angler is fishing on a stratified lake and putting all their effort at depths below the thermocline, the results will generally not be very pleasing. . . .
Another way to locate the thermocline with electronics is simply by cruising around and paying close attention to the depth at which the fish are marked on the display. If you motor around and see lots of fish congregated at and above 22 feet and see virtually nothing below that depth, it’s reasonable to assume there might be a thermocline at that depth."

Grumpy