How to Find the Thermocline Without a Fish Finder

The oppressing summer heat causes specific changes in lakes, reservoirs, and ponds that don’t have moving water. The sun’s rays warm the lake’s surface water, in the summer, creating thermocline – a thin layer of water that offers fantastic fishing opportunities. 

But how to find the thermocline without a fish finder? There are several ways to find a thermocline without using a fish finder. The thermocline layer looks like distorted glass and has a greenish or milky tint which can be seen underwater. An underwater swimmer would feel a dramatic drop in the water’s temperature after entering the thermocline layer. 

Knowing the thermocline depth is one of the most important things if you prefer to fish in the summer. Keep reading to learn how to locate the thermocline layer with or without using fish finders and other boat instruments. 

How Do You Find the Thermocline in the Water?

How Do You Find the Thermocline in the Water

Thermocline layers are generally found at depths of 10 to 40 feet. The water’s clarity depends on the depth of a thermocline layer. 

The thermocline layer will be closer to the surface in murky lakes, where the sunlight can’t penetrate the water’s depths. In lakes with crystal clear waters, the thermocline will be much deeper. 

There are different ways to find thermocline, including:

Using Boat Instruments

Finding the thermocline is fairly easy using boat instruments. Here’s how you can do it:

Use a Finely Tuned Sonar

A finely tuned sonar or a finder fish device can show the location of the thermocline. When the sonar is set on manual, and its sensitivity is turned to 90 percent, it will show the thermocline layer as a fuzzy line. 

If the sonar doesn’t provide the exact location of the thermocline layer, it will certainly show where the fish gather in the water. 

This spot is where fish congregate in the top layer of the thermocline. The fish finder will show the thermocline as a layer with many fish, both large and small, including schools of baitfish. 

Use a Temperature Gauge

Another way to locate the thermocline layer is to lower a temperature gauge into the water. At first, the gauge will show unchanging water temperature from the surface downward. 

But, when the gauge reaches the thermocline layer, you’ll notice a dramatic change in the water’s temperature. This means that you’ve reached the top layer of the thermocline. 

As you continue to lower the temperature gauge through the thermocline, the water’s temperature will continue to drop. You’ll know you’ve reached the bottom part of the thermocline when the temperature stops falling and levels out. 

Without Using Boat Instruments

The thermocline layer can be found without boat instruments, too. However, locating it without instruments is more in the realm of guessing the location rather than having evidence that it’s actually there. 

Here’s how to locate a thermocline layer without boat instruments:

Look at the Water’s Clarity

The thermocline layer is invisible from the lake’s surface to the naked eye. But, a visually acute person can identify the thermocline layer while swimming. 

In the water, the thermocline has a wrinkled surface and appears like distorted glass. It also has a greenish or milky tint because of the zooplankton that lives in this layer. 

Water’s Temperature

A diver can identify the thermocline layer by the sudden temperature drop. The surface of the thermocline layer is noticeably cooler than the water above it, and the temperature continues to drop with depth. 

Tips and Tricks for Thermocline Fishing

Since the layer of water beneath the thermocline is a dead zone where fish rarely venture, you should learn how to fish thermocline. During summer, most fish can be found in the top layer of the thermocline, which is rich in food and oxygen. 

Here are some helpful tips for fishing thermocline:

1. Fish the Upper Level of Thermocline

To increase your chances of landing a catch, fish the upper layer of the thermocline and around 5 feet above the top layer of the thermocline. Casting sinking lures or trolling through this depth can be very productive.

When trolling, use frequent turning motions to attract the fish. Use a countdown method when casting, splashing the lure into the water. 

2. Look for Fish in the Right Places

When fishing the thermocline, look for underwater structures such as wrecks, ledges, and rocks. Although some fish can usually be found around smaller underwater structures, you should look for larger alternatives when fishing the thermocline. 

Skip the smaller fishing holes, and look for larger ledges, underwater wrecks, and rocks to catch big fish.

3. Choose the Right Bait

The type of bait you decide to use will depend on personal preference, but you should bring some live bait. The waters above the thermocline are usually teeming with baitfish, making the predators spoiled and unlike to bite just about any lure. 

How Does Thermocline Affect Fishing?

The layer of water beneath the thermocline doesn’t have oxygen, and no fish can survive there for long. This is important information for all anglers who like bottom fishing. You won’t catch any fish if you cast a line in this zone, no matter how hard you try.

The best place to catch fish is just above the thermocline. These waters are rich in oxygen, and the temperature is just right for fish to thrive. The top layer of the thermocline is teeming with baitfish and other predatory species like bass. 


The summer is an excellent time to go fishing on a lake or a reservoir. Due to the brutal summer heat, most lakes, ponds, and reservoirs develop a thermocline layer, which is home to baitfish and many predatory species.

To increase your chances of catching a fish, you’ll need to find the thermocline layer. A sonar or temperature gauge can accurately locate a thermocline layer. If you don’t have boat instruments, you can locate the thermocline by looking at the water’s clarity and temperature.