O2 Content

[TENNESSEE NEWSOME]

I'm in Tennessee where the temps lately have been surging into the mid 90's.  In the sun, I heard it was over 100 at the airport today.

The oxygen content can't be that great in shallow waters far away from river/creek channels.  

Am I right to assume that in these hot temperatures, I should stick to areas close to deep water where the O2 content is higher?  Last time out about a week ago, the water temp was a blistering 85 degrees.

Also, if someone could answer this, it would really clear up something I have wondered for several weeks.  How much of a cool off is there from 0-10 feet, 20 feet, 30 feet, etc...  We have a number we can call for water temp, and the temperature at 10 feet is almost always within a half degree of the surface water temp.  At what point does it really begin to drop, and by how much?

[Low_Budget_Hooker]

It's not so much the temp that you need to be concerned with at different depths (10,20,30) but in deeper lakes, it's the thermocline.  When a lake flips, the cooler water is at the bottom but it is also the water with the least dissolved oxygen.  You want to aim near that 8-15 ft zone for consistent fishing in warmer water

[JShrock07]

In most lakes that have creeks running into it there will be a channel that carries the water. Once you find the channel follow it out to about 10 ft of water and fish that area. I agree with LBH when he says to fish the warmer water between 8-15ft. I read a while ago that there was a study done with a large tank, where they had a cool water aeretor on one side keeping the water very cold and a hot water aeretor on the other side just to find out what the bass like temp wise. They found that most of the bass stayed toward the side that had a water temp between 80-83 degrees.  8-)

[fishfordollars]

I am in total agreement with LBH and Nitroman. Many lakes are known for the lack of ozygen at the deeper depths. Perfect example would be Logan Martin in Alabama. Most of the fish are caught 1-15 feet due to the lack of oxygen in the deeper water.

If you will adjust the gain on your depth finders you should be able to see the thermocline. Try fishing the areas where the wind pushes plankton up in shallow water. It will increase the oxygen, put the fish in a more aggressive mood, and stir up the entire food chain. Remember, the wind is your friend, but most anglers avoid it. Good luck.

[WRB]

Find the thermocline layer and fish at that depth within a few feet.

The thermocline is a cooler layer of water that is more dense than the warmer water above it. You can see the dense thermocline layer on a good sonar unit as a dark line or fuzzy zone by using the manual settings. You can also determine the life zone where the bass and baitfish prefer to use by metering the bait depth, if your lake has threadfin shad for example, as they tend to stay close to the thermocline layer. The thermocline layer will be about 70 to 75 degrees with the surface water in the 80's. If the lake is a power generation lake, there could be 2 thermocline layers, so check depth down to 35 feet or so for baitfish and bass.

With surface water being in the 80's, avoid fishing areas near the surface during the day light period, unless the wind is creating wave action to aerate the surface water. Water at 80 degrees or more can't hold enough dissolved oxygen, DO, for bass to survive, so they go under the green weeds that produce DO and shade, or go deeper and just visit the upper hot water on short excursions.

If your are in a tournament, be sure you have ice to cool the water to around 70 degrees. Do not recirculate the surface water, add C & R chemicals and h202, 3% over the counter hydrogen peroxide; 1/2 cup for 15 to 20 gallons, will aerate the live well water to proper DO levels.

WRB

[Low_Budget_Hooker]

Find the thermocline layer and fish at that depth within a few feet.

The thermocline is a cooler layer of water that is more dense than the warmer water above it. You can see the dense thermocline layer on a good sonar unit as a dark line or fuzzy zone by using the manual settings. You can also determine the life zone where the bass and baitfish prefer to use by metering the bait depth, if your lake has threadfin shad for example, as they tend to stay close to the thermocline layer. The thermocline layer will be about 70 to 75  degrees with the surface water in the 80's. If the lake is a power generation lake, there could be 2 thermocline layers, so check depth down to 35 feet or so for baitfish and bass.

With surface water being in the 80's, avoid fishing areas near the surface during the day light period, unless the wind is creating wave action to aerate the surface water. Water at 80 degrees or more can't hold enough dissolved oxygen, DO, for bass to survive, so they go under the green weeds that produce DO and shade, or go  deeper and just visit the upper hot water on short excursions.

If your are in a tournament, be sure you have ice to cool the water to around 70 degrees. Do not recirculate the surface water, add C & R chemicals and h202, 3% over the counter hydrogen peroxide; 1/2 cup for 15 to 20 gallons, will aerate the live well water to proper DO levels.

WRB

Better info from someone who understands this better than many of us.  This is the info you want.

[Raul]

If you don 't have an upper quality fish finder that can detect and show the thermocline on the screen like WRB explained you can interpret what the unit is telling you by looking at how the fish icons that appear in the screen are distributed along the water column, if there is a thermocline then you will see fish icons above or on the thermocline layer but not below a certain depth in the water column, since the water below the thermocline is oxygen poor and the water near the surface is too warm fish icons will be "sadndwiched" between both and distributed in your screen, this tells you at which depths you should present your baits and which areas you should avoid and not waste your time, there ain 't nobody there.

[TENNESSEE NEWSOME]

I'm soakin all this up like a sponge.  

In the back of my mind, it seems like I read somewhere that the lake I fish doesn't go through the thermocline cycle...or maybe the lake flips opposite of others.  I fish Percy Priest most often where depths of 50-60 foot of water aren't uncommon.  If anyone knows thermocline info about it, please chime in.  

Thanks for the info.  This is great information.  

[Paul Roberts]

As I understand it, oxygen content in and of itself really isn't the problem with warm surface waters. There is enough O2 at 85F, or even 90F, for bass to live, however they'd need an awful lot of food to maintain body weight, much less grow, at those temps. Northern bass, anyway, appear to avoid these temps or at least may become inactive in them. I've always noticed that in most of the waters I've fished the bass become thin during midsummer.

Actually, if there is adequate plant growth (rooted or planktonic) O2 peaks during the day (bringing the water to saturation for the given temp) because photosynthesis accounts for the majority of 02 production in lakes primarily from rooted plants, secondarily from phytoplankton.

Oxygen deficits occur when oxygen use outstrips oxygen production. This happens in very nutrient rich waters, where accumulated organic material decays and the available O2 is used by more bacteria than fish. This is especially likely in turbid waters where light, and photosynthesis, is attenuated.

Over-nutrified waters often develop huge blooms of phytoplankton (and other algae) that then die off and create an oxygen deficit from the decay of all that accumulated dead algae. Rooted weeds die off at times too and it is possible, but rare I think, to have rooted vegetation creating much of an oxygen deficit alone. I suppose strong weed growth followed by suddenly muddied waters, or a large plankton bloom, with high temps, could cause an oxygen issue, especially in small waters or isolated coves that don't get flushed out by the main water body.

Oxygen depletion occurs commonly in the depths of fertile lakes where organic matter accumulates below the photic zone, above which photosynthesis can keep things humming. You can get a rough bead on how deep adequate light penetrates for plants is by the depth of the weedline keeping in mind that some plants require less light than others, and sometimes it's bottom make-up that limits where plants can grow. Suffice it to say that water clarity is the important factor in light penetration, and therefore, oxygen production.

A thermocline (colder denser water unable to mix with warmer wind affected surface waters) occurs far enough below the photic zone that photosynthesis cannot match decay and eventually oxygen is depleted. In clear lakes (with a deep photic zone), and not too much fertility, areas below the thermocline will have oxygen, and often more oxygen than surface waters because colder water can hold more oxygen than warm water does.

Thermoclines basically develop at a depth protected from wind action, which depends on the depth of the water body and how protected from wind by the land around it is. On a small pond deep in the woods, a thermocline could potentially develop as shallow as 8 feet. In a big open, wind swept lake it may not develop at all if the lake is shallow enough. Most thermoclines develop in lake basins at something approaching 20 feet deep and get progressively deeper through the summer, only to be ruptured in fall when surface temps cool and the density difference between the layers lessens. Eventually free mixing occurs, or, more often, a good wind finally ruptures it.

Oxygen depletion is not always a deep water phenomenon. It can also occur in stagnant over-nutrified waters, or backwater areas with no circulation from other areas of the lake. Here decaying material and little light penetration (excessive weed build up, algae blooms, and water turbidity) can feed the wrong critters.

Now, I've never owned an O2 probe (I know WRB has) but I'd venture that significant O2 depletion is relatively rare in all but the most over-fertilized waters, or fertile waters that are deep enough, and/or wind protected enough, to cap off the bottom waters in a thermocline. If your summer fishin' water has decent clarity and is not over-nutrified, oxygen depletion is probably not the reason bass are not feeding in midday in the shallows, or have gone deep. Heading deeper in summer occurs for reasons other than oxygen content. In other words it occurs even though there is sufficient oxygen in the shallows.

I'd love to have Bob Lusk weigh in on this topic.

[Gatorbassman]

You are right. Many lakes don't develop a thermocline for one reason or the other. When I fish a lake like this I concentrate on the water clarity and use the current to my advantage. After the sun gets up and it starts to get hot I take the water clarity and double it and fish that depth. So if I can see a white bait at 4ft I fish 8 to 10ft deep. I fish creek channels and points where channels make a sharp bend close to them. These places usually have more O2 then the still water will.

I was Senko77's boater at a Jr Bassmaster tournament last year. We were fishing a lake that has no grass and doesn't develop a thermocline because of the three rivers that run into this small lake. The rivers keep the water mixed up in this small lake. The air temps were above 100 and the water temp was 96. Our best spot was a main lake point. The river channel ran into the bank just before turning out and running along the side of this point. This created a large amount of current for this half of the lake. We went over it with our fish finder and it had fish stacked all over it. Long story short.. We boated several different species of fish there and he ended up winning the tournament by doubling the second place weight. It was a sweet spot. 

[Raul]

Excellent info Paul.  

Shallow water may not necessarily be oxygen poor but can have enough oxygen content for bass to be in it, down here where I live air temps can be easily in the 100 's, water temps can be in the 90 's, I can 't speak about other climates because my experience is limited to warm water environments. So why is it that you don 't find the fish in warmer water ? it 's the temperature, bass can survive in 90 degree water easily for extended periods of time, no they are not going to "burn" out, there are two factors to take in consideration:

1.- Like Paul mentioned, methabolic rate, the warmer the water the higher the methabolic rate, it means that the fish has to eat more in order to maintain it 's organism running.

2.- Comfort zone, bass prefer water in the 70-75 degree range, not only it 's methanolic rate is tops at that temp it 's also that they feel comfortable at that temp. It 's just like us, where would you rather be, getting fried at 100 degrees or being in your house with the AC on comfortably sitting on the couch at 65-70 degrees ?

Fish go deeper where the cooler water ( which also has a higher oxygen content ) is or in the shade to be comfortable, that 's why you don 't find them where the water is warmer.

[Paul Roberts]

Quote

The air temps were above 100 and the water temp was 96. Our best spot was a main lake point. The river channel ran into the bank just before turning out and running along the side of this point. This created a large amount of current for this half of the lake. We went over it with our fish finder and it had fish stacked all over it. Long story short.. We boated several different species of fish there and he ended up winning the tournament by doubling the second place weight. It was a sweet spot.

Very8-)

It would be interesting to check that area with an O2 meter, the surrounding area, and the incoming trib. For the future, it would be worth knowing whether it was oxygen or the physical effects of current that made the difference.

This makes for a good discussion example because current is often misunderstood in effect, as is shade. Not to say that Gatorbassman is misunderstanding anything, or wrong in his assumption a grass-less but highly fertile res could be well below oxygen saturation in midsummer. And doubling second means you were onto something special. Just out of curiosity, was that res at very low pool?

But, in many cases, temps (or oxygen), may, or may not, play the role we might think it does. Current to a fish, and a cool breeze to a mammal, are not synonomous.

Current, in and of itself, does not often provide more oxygen in most commonly encountered situations. Current can bring oxygen, under certain circumstances, but I think its effect is generally overrated in most waters, except maybe in some very fertile, vegetation-limited, reservoirs.

Some examples:

Wind generated currents, just pushing around the same temp water, won't add oxygen. Maybe rolling up deeper colder water might (cold water can hold more 02), if there's oxygen down there to bring up at all. But that would be quite a blow, and we'd be dealing with other stuff at that point, and would soon enough go back to the norm.

The other way to add oxygen to water (besides dropping the temp and photosynthesis) is to churn it up with air because air holds a lot more oxygen than water can. A strong blow might do this, but only if the affected water was already well below saturation, and the effect would be short-lived as the processes that made the area sub-saturated would likely still be in effect.

For a current from outside a stillwater body to bring in sufficient oxygen it would either have to be coming from a much colder tributary, large enough to alter the water temperature of that area of the res. Or, that area of the res would first have to be well below saturation having those use versus production issues mentioned. This is not unlikely with a grass-less but highly fertile res in midsummer, when biological activity (oxygen use) is in high gear. But I would expect that that trib would have to be large and moving water through at a good rate to really have much effect.

Maybe T9 can weigh in -he may even have some real live data.

In general, current has other, more general and profound effects: Incoming tribs are important for the basic development of the food chain in many phytoplankton-based fisheries. Also, current can concentrate and orient the food chain, creating easier feeding opportunities.

Shade is commonly misunderstood too it doesn't affect oxygen levels (except maybe to decrease it by hindering photosynthesis). Instead, shade serves to get overheated bass out of the direct heating effects of the sun, is a safe place to rest in poor conditions for hunting, allows a closer approach to prey when hunting, and helps obscure the ridiculous nature of our FAKE lures. It doesn't affect oxygen levels.

Raul touched on an important point: Optimum growth temperature (determined in the lab) is not the same as preferred temp.