Dissolved oxygen levels?

[dac]

I keep a close eye on the Corp of Engineers water quality report each time it updates(about once per week) to check the dissolved oxygen levels at my home lake. What I cannot figure out is why I catch fish so much deeper than the chart would lead you to believe is possible? For instance, the other day the dissolved oxygen levels were reported as average to good(5ppm plus) down to 15 feet deep, and then they dropped off to 3.2 ppm at 16 feet, and less than 1 ppm below that. The reading was taken about 9 am and reported later in the day. I believe the reading is taken at the lower end of the lake near the dam, which is the deepest part(down to 100 feet in places) of the lake and has cooler water. On the evening of the same day as the latest reading, and mind you it had been hot with very light wind all day, I am catching bass on the bottom in 18-25 feet of water around dusk, and marking many fish near the bottom all the way down to 30 feet deep. Is this because the reading was taken early in the day, when there is the least amount of dissolved oxygen in the water, and I am fishing in the evening, when D.O. levels are the highest, and the depths have more oxygen at that time? Can the D.O. levels change that much each day? I am generally doing my fishing on the lower end of the lake within a couple miles of the dam, and doing it in various places/spots. And believe me, this is not just simply a case of miscalculation of how deep I am really fishing. Could it be that some of the spots I fish simply have more oxygen at deeper depths for some reason? I want to understand!

[Fishin is life]

During the summer months I always catch fish deeper than I should according to the chart....Just because the fish might be in 20ft it doesnt mean they cant suspend up off the bottom 5ft and be in the right oxygen zone.....I can't give an exact reason for why they are down there but they always seem to be in the hot weather

[mkmsports41]

I would have to beleive the thermocline has more to do with them being deeper than the reported oxygen level. The thermocline may be at 20ft. Therefore the water temp may be 10d cooler at 25ft than it is at say 15ft. Next time your out determine the thermocline. It is realitively easy to determine. I like to get in the deeper end of the lake and just watch my graph. If you are graphing all your fish in 20ft of water it is safe to say the thermocline is slightly above that level.

[TimE]

I would have to beleive the thermocline has more to do with them being deeper than the reported oxygen level. The thermocline may be at 20ft. Therefore the water temp may be 10d cooler at 25ft than it is at say 15ft. Next time your out determine the thermocline. It is realitively easy to determine. I like to get in the deeper end of the lake and just watch my graph. If you are graphing all your fish in 20ft of water it is safe to say the thermocline is slightly above that level.

I would have to disagree. Fish should be above the thermocline as the temp and oxygen levels are at a happy medium. Below the thermocline is the dead zone.

[dac]

MKM, I realize what you are saying about the thermocline with the right temps and oxygen, but regardless of where the thermocline is or is not, I should not be catching fish 25 feet deep according to this chart. From what I have always read fish cannot survive in water with dissolved oxygen levels less than 3-5 mg/L. By the way, in my original post I was using the wrong measurement abbreviation, as I was using ppm instead of the correct mg/L-my bad on that if it confused anyone. Anyway, here is the chart I am referencing:
Depth Temp Oxygen
0 86.0F° (30.0C°) 8.5
5 86.2F° (30.1C°) 8.5
10 86.4F° (30.2C°) 8.3
15 84.7F° (29.3C°) 5.3
16 82.2F° (27.9C°) 3.2
17 81.5F° (27.5C°) 2.1
18 80.1F° (26.7C°) 0.4
19 79.0F° (26.1C°) 0.2
20 77.4F° (25.2C°) 0.2
25 76.6F° (24.8C°) 0.1
26 73.8F° (23.2C°) 0.1
27 71.8F° (22.1C°) 0.1
28 70.7F° (21.5C°) 0.1
29 70.3F° (21.3C°) 0.1
30 70.9F° (21.6C°) 0.1
31 67.5F° (19.7C°) 0.1
32 66.9F° (19.4C°) 0.1
33 66.6F° (19.2C°) 0.1
34 65.5F° (18.6C°) 0.1
35 66.9F° (19.4C°) 0.1
40 64.6F° (18.1C°) 1.1
45 62.1F° (16.7C°) 0.7
50 59.9F° (15.5C°) 1.4
55 59.0F° (15.0C°) 1.5
60 58.5F° (14.7C°) 1.4
65 57.9F° (14.4C°) 1.4
70 57.2F° (14.0C°) 0.7
75 57.0F° (13.9C°) 0.5
80 56.7F° (13.7C°) 0.1
85 56.3F° (13.5C°) 0.1
90 55.8F° (13.2C°) 0.1
95 55.8F° (13.2C°) 0.1
100 55.6F° (13.1C°) 0.1

According to this chart, there should be no fish below 15/16 feet. The very same day this chart was measured and recorded, I am catching them as deep as 25 feet right on the bottom straight over the side of the boat and marking fish as deep as 30 feet. This was only a few miles from the dam where I believe the readings are taken.

[mkmsports41]

Well since you said you were near the **** you may need to take into consideration the current. Maybe the measurements were taken with a slack current. Not sure what body of water you are referring too but maybe the **** was not open or not generating at the time.
Or possibly the fish just have not moved yet. I have read several articles and actually seen several print outs of Lowrance and Hummingbird units where you see fish well below the thermocline. The thermocline and oxygen levels are one in the same. The best way I have had a thermocline described to me is that the Thermocline happens when oxygen levels deplete and seperate the water column into two different levels. There will typically be a difference in water temperature at this point as well. Fish will often sit at this seperation point as water temperatures and oxygen levels are most suitable.

[kygorski]

Much of what we know about thermocline comes from fresh water natural lakes.Also water clarity. weed growth and current entering or leaving a lake have to be considered. But one thing to consider, fish dont read!

[98zr2]

My understanding is that the thermocline depth can vary on a lake especially when you have a wind driven current pushing water one direction pushing the thermocline down deeper

[roadrunner]

I had a fish biologist tell me that a fish can not live below the thermocline because there is not enough oxygen to support them. However he said I know you can catch fish below that depth which tells him they can go below this for short periods of time maybe 15 minutes maybe an hour he did not know but he did know that he has caught fish lower that the thermocline. My question is if they go down their why are their minnows living that deep? I don't think so are they going down becuse it is cooler and it lowers their metabolism and they will eat something if it is there (your jig). With that said you would think that fishing a foot above the thermocline would be the best fishing.

[artcarney_agr]

Maybe the fish goes down into the "dead zone" because he felt the vibrations of your bait down there and felt the need to check it out?

[TimE]

Maybe the fish goes down into the "dead zone" because he felt the vibrations of your bait down there and felt the need to check it out?

I agree with you and Roadrunner on this. Maybe thats why big worms and crankbaits work so good this time of year.

I have caught fish on a drop shot or spoon directly under the boat in 25' of water and in that case i believe that the fish were suspended above the T-cline and followed my bait down. Also read of people running over brushpiles with their big motor to spook the fish into them so they could key on them easier. Interesting subject!

[peter]

According to the chart the thermacline is at 25-26. The greatest change in temperature. However, I think your question is more related to o2

I'm not sure that 02 and thermacline are locked in there together. 02 depletion below the thermacline gets worse as summer continues because the layer above and below the thermacline do not mix so the 02 below is not replaced.

I would guess there are pockets of 02 in any given lake and I just yesterday saw the thermacline swing fron 40' to 70' within a few miles and hours (according to my graph and how read it). Find the pockets, find the fish. Maybe you have. I have seen fish stay in low 02 to have a cooler temp but 0.1 is almost nonexistent.

My guess is that these readings can only be used as guides. Nothing I have found in fishing is absolute.

If you are catching fish...you're doing it right.