Seasonal Issue: Low Dissolved Oxygen and Restricted Flows

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Many issues to talk about, as well as fishing, in the fall. Dissolved oxygen, water temperature, restricted flows…… confusing details to understand when fishing tailwaters. Wish we didn’t have to consider them when JUST fishing, but they do affect the way trout move, hold, feed– and don’t feed– and that affects our fishing strategy.

I know this is old hat to some of you, but I’d like to go over the basics. Lakes change at different seasons of the year. As spring and summer pass, surface water warms and separations or layers form. Because water density changes when it differs in temperature, these layers become very defined as summer wears on. If you look at the Lake Profile - http://www.swl.usace.army.mil/wcds/rdo2.html you will see a profile, kinda of a photograph, of the water at the dam at Table Rock. See where the temp drops, as well as the DO level, as it gets deeper. And the big drop near the top - this is called the thermocline and where, generally, a large number of fish will hold. As the water warms on the surface, the thermocline drops lower in the lake. We get our water at 130 feet deep and is marked by an asterisk to the side. As you see, the water temperature is colder at that level than the surface but the DO is very low and gets lower as you drop down. As colder weathers rolls in– November and December– surface temperatures drop, literally. Cold water is heavier than hot water and thus drops and “turns” the lake over at some point in the game. It’s like a tilting table: when the load on top gets heavier than the load on the bottom, it tilts and turns over, leaving the heavier on the bottom. This happens generally from around Thanksgiving into December. Until then, we’re stuck with low DO levels entering into LT.

What does low DO do to our trout? It slows them down a bit. How do you know when DO levels are too low and threaten the life and health of trout? A high number is 12 parts per million (ppm). A low number is 0 ppm. Generally, fisheries biologist say 3 ppm is the bottom on the scale, and with high water temperatures, could cause death if prolonged. Six ppm is what the State of Missouri Clean Water Act says is the standard for “safe” water. But the Corps, as a federal agency, doesn’t have to adhere to state regulations and has set its mark at 4 ppm. Are we happy about this? No. We’ve appealed for change but to no avail– yet.

The Corps does put restrictions on flow at Table Rock. These flow restrictions differ as the fall months progress and the water quality drops. This just means that even in peak times, levels will not exceed the ability to add enough DO to the effluent to keep levels above 4 ppm.

There are three ways dissolved oxygen is added to the near-nil levels in September and October. The hatchery outlets are rich in DO. That’s why you will see large numbers of trout with their noses in the effluent. The Corps has modified the turbines and added vents at the top of the chambers to allow air to mix with the water, creating a sloshing effect as it enters the lake. This is hard on the turbine blades, causing the surface of the blades to weaken. Corps officials like to reminds us about this — that they are sacrificing for the good of the trout. When all of the above fails to add adequate DO to the tailwater, the Corps injects liquid oxygen directly into the turbines, a very costly procedure. Monitors keep track of DO levels as they enter the lake. All this for a few fish below a big man-made dam.

One thing you have to realize– when the federal government build dams, bureaucrats have to promise that the dams won’t hurt the fishery in either the lake above or the tailwater below. When they build dams that are high and the water coming out is too cold for warm water species, they have to provide coldwater species for that fishery, such as the Neosho Federal Trout Hatchery producing 200,000 rainbows per year. Water quality standards also have to be maintained at a level the fish can survive and thrive. The definition of thrive is in question here. The Corps’ definition is to “just get by.” Sportsmen and fishing-related businessmen think thriving means the fish “move and grow respectively, with adequate food supply to reproduce.” But the food supply is low, and there is no reproduction. That must change, and I believe it will in time.

What’s going on with the fishing?

Autumn is one of my favorite times to fish Taneycomo. Why? Dry action. Browns moving up. Water generation slows to levels that are fun to fish. Night fishing below the dam. Fewer crowds on the water. Jig-n-float fishing gets real hot. Milder temperatures. Fog lessens in the mornings and evenings. Leaves start to change, and the scenery becomes breathtaking!! Enough reasons?!

First below the trophy area: July fishing was really slow. The beginning of the cold water, after so many days of warm water due to no generation, seemed to be the beginning of the slow fishing. The Missouri Department of Conservation was stocking the usual 90,000 rainbows, but they were stocking mostly in the mid- to lower lake. We were sending guests down to the bridges in the Branson to look for trout which is usually unnecessary. Dock fishing was hit-and-miss. Powerbaiters struck out most of the time, and nightcrawler anglers caught a few.

Fishing did rebound in August. Our guides have reported doing extremely well using inflated nightcrawlers on the flats above Short Creek, catching a few, very nice, colorful rainbows. Jig-n-float fishing has also been good in the same area using 1/100th jigs in olive, black/yellow and pink, two- to four-pound green line and fishing three- to six-feet deep. Remember trout usually won’t take the float under– they’ll just tip or vibrate the float. You have to be quick on the set. If you’re missing strikes, trim the marabou tail.

What to expect this fall: Browns will be on the move. Throwing jerk baits, hard and soft, could be very rewarding. Buster Loving is one of our guides. He competes in quite a few bass tourneys during the year and does very well. His favorite bait is a suspending rouge, and the funny thing about is that he throws it just as much to trout as he does for bass. His start-and-stop action sometimes draws a strike when a lot of times you only see follows. I’m amazed when fishing with Buster how he works a rouge. He jerks the bait down wildly, then pauses, then “pops” the bait three to six times and lets it sit. He’ll let it sit suspended for 10 to 15 seconds, drawing strikes at anytime the bait is dead in the water. Sizes- medium length. Colors- purple with a white belly, chartruese or all white.

When the water is running, bouncing jigs off the bottom and along steep banks will draw big strikes and big trout. Use 2-pound line and 1/16th oz white, black, sculpin, grey or olive marabou jigs. The first 500 yards below the dam during the spawn is the most productive. Second best would be the Big Hole area. Also the Clay Banks and the stretch below Lookout should be excellent.

In the trophy area: Good fishing. Lots of small rainbows to deal with though, which seems to be the biggest complaint among those who fish up there. But the trophies are up there — take my word for it. If you don’t want to take my word for it, ask some of the MDC guys who just finished their annual sample on the upper lake. One of the guys said he handled seven browns longer than 24 inches, the biggest one about 27 inches. Others said the browns looked very healthy while the rainbows were a bit thin. The results of the sample will be ready by the end of September. As soon as I receive them, I’ll pass them on.

Reports from the fly water just below the dam are good. Seeing plenty of nice trout, but in bright, sunny, still days, they’re a little hard to hook. Our trout will hang close to the hatchery outlets for a couple of reasons. The quality of the outlet water is high in DO, and the riffle effect gives the trout cover. So you’ll see a crowd most of the time at each of the three outlets, most at #1 and #2. The rebar shoot and hole will hold tons of trout…. and anglers too. The places I seek when I fish below the dam are the places where no one thinks to fish. For that reason, the pressure on those places is much less, thus the trout are less spooky. Read Ryan’s piece about midges later in this issue. Be observant of the water before you start fishing.

Dry action is just starting to heat up. The heat has driven bugs to the water and our trout are loving it. During generation, high water floods islands full of weeds and wild flowers. These flowers are full of bugs, especially butterflies. As I fished this week, in the mid-afternoon heat, I notice butterflies floating out of the weeds and being chomped on by waiting rainbows. A yellow humpy was the trick. And on every cast for an hour, I either had a strike or a look. Along another bank I found where the weeds were flooded, anchoring the boat above the area and drifting the humpy down through their feed slot, another productive 30 minutes. It’s only going to get better!!!! You really need to try this!

Hatchery personnel report browns are already starting to show up in the “ditch.” The ditch is the top of outlet #3 where browns swim thinking they are going up to spawn. Ironically, they will spawn, but not in the way anticipated. They will be taken within the next few weeks by net to the hatchery where they will be drugged, stripped of their eggs and sperm and returned to the lake. Sounds romantic, right?! But the point made is that they are starting to arrive a little early this year. Is that a sign for the rest of the spawning season? Who knows. Will just have to keep an eye on it.

Water temps coming from Table Rock are six degrees colder than this time last year. That’s good news for the hatchery and the lake. Last fall, along with the low DO we had high water temps, which put our trout in additional stress. The colder temps should help the trout endure the fall months better. I really do look for an exceptional fall season. Hope you can get away and enjoy part of it.

Another version -

Dissolved Oxygen

For those in the know on the DO issue in Lake Taneycomo, I have great news so far this fall season. The dissolved oxygen in our tailwater has stayed at good, safe levels. Even compared to past years, the levels are extremely good. This observation comes from the reading reported by the Corp at their site at http://www.swl.usace.army.mil/wcds/rdo2.html. I have kept track of the readings on most days, and they have stayed up above 6 parts for most of the day and night. If you follow the readings, you’ll notice the best DO we experience is at high noon- better sunlight means higher DO- especially in the extreme upper end.

For those who don’t have a clue what I’m talking about, here’s a quick DO course…

Water contains oxygen, H2O - O stands for Oxygen. Oxygen is measure by parts per million. On a scales of 1 to 12, 12 is about the highest you’ll find in lake water- usually in the top layers where sunlight, wind and rain adds oxygen. In any lake or pond during the seasons, the layers form layers. Each layer has different density and oxygen levels, depending on the season and temperature of the water at the different levels. The layers start forming in late spring when the top levels start to warm. As summer rolls on, temps in the upper layers really rise and becomes lighter then the layers below. Because of the lack of sunlight, oxygen levels drop as you get lower in the lake or pond and later in the fall, DO amounts at the bottom are nile. As it gets closer to winter and the air temps drop and winds pick up, the surface temperatures drop also. Cold water is heavier than warm water thus this cooler water sinks to the bottom. This starts the the turning effect. When alot of water on top become cooler than the bottom- heat rises- the two levels mix and thus- good DO throughout the depths. The the cycle starts all over again. Clear as mud?!

As far as the different levels- 0 - 12…… where 0 is real bad (no oxygen- things die) and 12 is usually the surface reading on a lake during alot of wind- may be even 13. The State of Missouri has said that anything under 6 parts is considered pollution. If a business or private individual discharges water with a lower reading than 6- they could get in trouble. But since a dam and the water it releases is not considered “point source” discharge, these rules do not apply and cannot be enforced. The Corp’s low point is 4 parts- they try and not go below 4 when they release water from Table Rock. Fisheries for MDC has said that 6 parts is a good bottom indicator– where fish and other water creatures can live, feed and reproduce. They also say anything below 3 parts can and will cause death in most trout, but this depends on water temperature also. Stress is the key. If a rainbow is already in stress because the water temp is above- say- 60 degrees and then he’s hit with low DO- say 3 or even 4 parts, he could die. And the bigger the trout is, the more stress all these factors affect it.

Our water this fall hasn’t gone much under 6 and our temp has stayed under 54 degrees- excellent!! In lean years or years when there’s higher water temps- I tend to watch the graphs real close. We have had fish kills during the fall months. But this year should be a good one for our trout- and for our fishermen.