Around the end of May or the first of June, the thermocline, a thin layer of water sandwiched between an upper epilimnion layer and lower hypolimnion layer, sets up when the water temperature reaches aproximately 73 degrees. During the hot summer months, there are three distinct temperature ranges from 0-12 ft, 12-22 ft and 22-45 ft with an approximate 10 degree drop for each depth range. Lakes of 15 ft and less do not have a thermocline because there is enough sunlight to support photosynthesis and phytoplankton growth at all depths. Lake clarity and strong winds can change the depth of the thermocline.

Because the lack of sunlight and decay of organic materials on the bottom, the hypolimnion lacks oxgyen and vegetation growth. Plant life doesn't grow well below 30 ft. However, there are times when the hypolimnion can hold fish because currents, strong winds and feeder streams can bring high levels of oxygen to this layer and fish will follow. In the fall when the surface temperature drops, the surface water sinks to the bottom and the warmer bottom water comes to the surface and is called "turnover." The water may smell like rotten eggs (hydrogen sulfide gas) and there will most likely be a shad kill. This is nature's way of fertilizing the upper levels of water.

Why is this important to the bass fishman? First of all bass like the thermocline because there is too much light in the epilimnion and too little oxygen in the hypolimnion. In late spring, early summer after the thermocline sets up, and post-spawn is over, predictable fishing returns in water depths of 12 to 22 ft. Bass fishermen should only be concerned with thermocline and above, and more specifically, the "sweet spot" from the thermocline to 5 ft above. Usually, bait fish and bass will be together in this zone.

October is the month with the most temperture changes. Water temperatures become more uniform from the surface to approximately 25 ft, varying from 70 to 65 degrees around 22 ft. In early October, bass like to be in the upper region of the thermocline, and the thermocline can be as much as 7 to 10 ft thick at that level. When this happens, bass fishing improves greatly. After turnover, bass become active and can be found anywhere from chasing shad in coves to suspending over humps and points in pre-winter patterns.

In closing, if you can find where the thermocline touches a point or deep structure, you are in a "true thermocline sweet spot." In the coming year, play around with your gragh in increasing the sensivity function of your sonar to around 90% and track the location of fish to the thermocline. A lot of times the fish we see do not bite, but I would rather be fishing where I know they are than beat the banks with out fish. Good fishing everyone!