Understanding Thermoclines


Summertime is known for catching bass in deep water, the big question is where do I start. One big key to catching bass when the weather is hot is to find the depth the fish are using. My favorite starting point this time of year is the thermocline.

The thermocline is somewhat of a summertime oasis for not only bass but many species of fish.

The thermocline starts to form in the spring on calm, warm days. During these days, the upper layer of water warms while the lower layer of water remains cold. Since cold water is denser than warm water, the cold layer remains on bottom. As spring and summer progress, the temperature difference between the top and bottom grows to such a degree that the two form two distinct layers. The upper layer is warm, high in oxygen, and low in nutrients.

While the lower layer is cool, low in oxygen, and full of nutrients. Between the two is a thin layer where the two mix, and this is the thermocline.

In this thermocline layer, conditions are outstanding for algae growth. The result is an algae bloom. This is the basis of why the thermocline attracts bass. It is no more than a process of the food chain.

Algae attract zooplankton, zooplankton attract baitfish, and baitfish attract bass. This algae bloom can often be seen on a depth finder or LCR unit.

The thermocline forms at different depths depending on many factors such as: water clarity, current, water depth, etc. On my home lake (Table Rock Lake), the thermocline generally forms around 30 feet. In clear water the thermocline can form much deeper. Keep in mind not all bodies of water have a thermocline, it is very prevalent in deeper reservoirs. I have caught fish as deep as 70 feet following the thermocline.

Once you establish where the thermocline is, just find some sort of structure at that depth and start fishing. A couple of my favorite techniques for this situation are fishing a heavy jig and a Carolina rig. I usually start with a 1/2 to 3/4 ounce black and blue or Green Pumpkin Football head Jig. I like to fish it on a 7 foot Worming/Jigging rod with 15 pound test Stren High Impact. I do prefer to use pork when this is my primary bait and I am keeping the bait in the water.

My choice of pork is a Bo-Hawg Jr. cut. Also you might try a white jig since the bass are primarily feeding on baitfish at this time. A sharp jerking motion off of the bottom often triggers strikes around the thermocline.

When I pick up the Carolina rig, I generally use the same rod and line combo and a 3/4 or 1 ounce weight. My baits of choice are Flippin Tubes and grubs and spoons, all of which represent baitfish well. One trick you can employ is to stuff the tube with styrofoam causing it to float off the bottom. Also try sliding a spoon inside of a tubebait. This is particularly effective for smallmouth and suspended fish.

As the summer heats up, don’t let the fishing cool off. Follow the food chain to the thermocline and enjoy.