How to spot thermocline on the lakes

Published 12:01 am Sunday, August 17, 2014

That was a nice week considering it is August. Air temperatures during the early morning hours felt great.

Reports on the fishing are still mixed up. The bass bite on most of the landlocked Louisiana oxbow lakes has slowed down, but you can still have a fair day of fishing on those waters. Target the shade in the shallows and forget the deep water bite. The thermocline is near the surface on the landlocked oxbow lakes.

That means there is no oxygen in the depths. It is like that every summer. As the water heats up, the thermocline begins to rise. Game fish, well almost any species of fish, cannot live below the thermocline. Catfish in still water lakes, where there is no current, can somewhat tolerate low oxygen content, but the bass, perch and bream cannot.

The fish will move up and hang under the thickest cypress trees they can find that offer the most shade. Piers with the main platforms built low to the water offer more shade than platforms built high off the water. That is where the fish are, but getting them to open their mouth is not easy. The game fish feed more at night than during the daytime with the exception being cloudy rainy days. On the unprotected side of the levee they live in, oxbow lakes we call Old Rivers are still producing some nice catches for some and nothing for others. As odd as it sounds, the best reports I heard are coming from shallow water. That may be because the Mississippi River was holding pretty much steady around 20 feet at Natchez.

That kills any current so a thermocline will develop. I plan to check on that today. It is easy to find the depth of the thermocline with even a cheap sonar unit. The mid to upper end units will show the thermocline as a shaded area on the screen.

On the cheaper units, you can see this shaded area and you disable the automatic sensitivity mode, go to the manual mode and increase the sensitivity level and ping speed. Another way to see the thermocline on sonar is rough fish. If you notice the rough fish, meaning buffalo, gar, carp and even shade, hanging at a certain level suspended off the bottom, you are looking at the thermocline.

On the Old Rivers, the thermocline is usually a bit deeper than it will be on the still lakes. During the summer, that is a quick way to eliminate a lot of water. Locate the thermocline, and you can forget any depth below it.

Here’s an update. As I type in my office, a great longtime friend walked in to give me a fishing report. Victor Bongiovanni and Jimmy Hodges fished Old River Saturday and had a good day fishing for bass. Out of respect to both my friends, we go back 40 years, I am not saying lure, location and all, but I will say they boated some fine bass on Old River. That is fresh news and thanks Mr. Vic. That was good timing.

The river prediction at Natchez looks good for the next few days. Today we should be around 19.6 feet. Monday through Wednesday’s predictions look like this; 19.2, 19.0, and 18.8 feet.

At this level, the Old Rivers will remain connected to the Mississippi River. That is a good thing.


Eddie Roberts writes a weekly fishing column for The Democrat. He can be reached at