Understanding the Thermocline in Lakes
By Marc Rogers
Discussing the Thermocline can be a very detailed and scientific subject. However, for this the basics will be covered in how the Thermocline relates to the behavior of bass. From spring to fall the Thermocline affects bass behavior in several ways.
In late spring the surface water in most lakes has warmed into the low 70-degree range while the cooler water is well below the surface. Surface water in this temperature range still holds plenty of oxygen so the bass have not yet started to migrate into the deeper water. However, as the surface temperature rises into the low 80-degree range, bass will seek the cooler water that holds more oxygen. The warm surface water doesn’t hold enough oxygen to keep the bass comfortable and this is when they seek the deeper water.
The Thermocline is a small area of water that lies between the warm surface water and the deeper water that also holds little oxygen. Most of the time this small area of water is only about ten feet from top to bottom. In the deep Ozark lakes there are sometimes exceptions to this rule and the Thermocline can be up to thirty feet from top to bottom.
In mid-summer largemouth bass will generally hold close to cover and/or structure near the upper edges of the Thermocline. When an angler finds the Thermocline this is great starting point for the proper depth to locate bass. A depth finder with the sensitivity turned up makes the Thermocline visible on the display. It will look like a false bottom reading on the display.
At Lake of the Ozarks the Thermocline will generally be found about 25 feet deep and only reach down to about 35 feet. In Table Rock Lake – a much clearer body of water – the Thermocline generally starts about 60 feet deep and can extend to about 80 feet deep.
Lake of the Ozarks is best fished during the summer at night due to the amount of boat traffic during the day. The Thermocline still hold at the same level and should be the targeted depth for bass fishing. June through August is best fished with a bottom-bouncing lure like a jig, plastic worm or heavy spinnerbaits. However, most of the time the bass will only be active near the Thermocline.
Table Rock Lake is best fished at depths of 60 – 80 feet deep since this is the depth where the summer Thermocline is generally located. There are only a few effective means to get a lure this deep. A Carolina rig can be fished this deep. However, my favorite is to vertical jig a small plastic worm on a ¼ ounce jig head or a jigging spoon presented at the required depths to reach the bass.
Spotted (Kentucky) bass will suspend just above the submerged treetops that are still abundantly available in Table Rock Lake. They will school together at the same general depths most of the summer so once located they are easier to follow at later times. Again, the key to this location is the Thermocline affecting the behavior of the bass.