Tuesday, February 27, 2024

What is the lake’s thermocline layer, and how should anglers deal with it?




As a licensed professional fishing guide, Michael Acosta shows you how to find them. A Granbury resident of more than 35 years, he has been fishing all of his life, and has been a licensed guide since 1998.

For the past couple of weeks due to the heat, many Texas lakes are stratifying, which sets up three distinct layers of water on our shallow Texas waters. Currently here on Lake Granbury, the thermocline is between 15 and 20 feet and hopefully this discussion will help.   

The thermocline is a layer of water somewhere within the water column where the warmer upper waters are prevented from mixing with those at a deeper depth.  This barrier prevents the interchange of nutrients between the two areas, which creates essentially two separate environments in the same body of water.

In a water column that is stratified, the thermocline is an area between the warmer water up to the surface called the epilimnion and the cooler water below called the hypolimnion.

The epilimnion is the upper layer that stays relatively mixed and the temperature is relatively constant throughout its region.  The thermocline is generally a relatively shallow region between the epilimnion and the hypolimnion, where the temperature change is relatively large.

The hypolimnion is the lower layer of water whose temperature is relatively constant.  Life is scarce in this hypolimnion region, as sufficient food and oxygen may be in short supply.

The thermocline is important to angling because it represents the deepest, coolest, oxygenated water for the fish to survive in.  It is where most species migrate to and stay in during hot water conditions except for transient feeding activities.

Different lakes will have different levels where the thermocline exists.  Different areas on the same lake may have different levels where the thermocline exists.  Generally, most sonar graphs will show the thermocline.  You may have to increase the intensity to see it, but it will show it as a dark area resembling constant debris/clutter.  Consult your instruction manual as they usually have pictures of what a thermocline should look like on your graph.  Many of us striper fishermen using live bait will find the thermocline real quick when you realize that your live bait dies quickly at a certain depths.  Deeper lakes like Lake Whitney will develop a deeper thermocline typically 20 to 30 feet or so.  When fishing live bait, your bait will suffocate if you lower into or below the thermocline.  On shallow lakes like Lake Proctor, the thermocline can be as shallow as 10 to 12 feet down.    

The thermocline can change with the influx of fresh water or heavy wind, which can mix up the water.  As long as the water stays warm and continues to heat, thermocline will most likely be present.  Some shallower lakes or ponds apparently may never develop a thermocline.

Use your electronics to locate fish.  The thermocline will congregate fish in the top level of the water body, making it easier to locate them.  Now, getting them to bite is another story.  Try several different patterns and different sized baits.  Stressed-out fish may be more apt to hit small bait.   If you troll, set your depth right at the thermocline.  You may be able to find active fish by running your baits all along the thermocline level until you can find an active fish.   Don’t be afraid to chum the water with diced shad as this may bring on the striped bass bite where nothing else will.  

Concentrate your efforts around this thermocline in the summer, and your chances for catching fish will most likely improve. 


Water temperatures are in the upper 80s on the main lake and in the 90s in the shallow sloughs.  Striped bass are being caught real early on live shad in Striper Alley on the lower end.  Sand bass are good trolling spoons or rattle traps.  Some sand bass schooling is occurring near DeCordova on the flats.  Black bass reports are fair to good early on topwater and crankbaits and later near deeper docks and main lake points and in the river near laydowns.  Blue cats continue to be good in the evening on cut shad.  Crappies are good to excellent near bridge pilings and submerged structure about 10 to 15 feet down.      


On other reservoirs, Lake Whitney striped bass limits are coming early on live bait. Possum Kingdom Lake striped bass to 18 pounds are possible and largemouth bass to 8 pounds are possible mid-lake to the lower ends.  Look for topwater action early.       

michael.acosta@att.net | 254-396-4855