Skip to main content

Find the Thermocline for Better Summer Fishing Success

Find the Thermocline for Better Summer Fishing Success
Find the Thermocline for Better Summer Fishing Success

FRANKFORT, Ky. – Fishing instruction for decades preached anglers should fish deep, cool water during the hottest days of the summer.

This makes sense as fish are cold-blooded animals and their bodies are the same temperature of the water that surrounds them.

However, fishing deep water in summer on a lake such as Taylorsville Lake may mean your offerings are in a dead zone. Warming air temperatures change the nature of the water in a lake. Anglers need to consider these changes while summer fishing.

The water column in lakes begins to stratify in late spring, like a layer cake with a warm top layer, a mixing layer in the middle and a cold layer on the bottom. Warm water is less dense and sits on top of the cooler and denser water below.


“The mixing layer in the middle is the thermocline,” said Dave Dreves, assistant director of fisheries for the Kentucky Department of Fish and Wildlife Resources. “The thermocline is a band of water with rapidly changing temperatures.”


As summer progresses, the water below the thermocline grows increasing hostile to fish. “As organic material from plants or animals sinks to the bottom, decomposition ties up all of the available dissolved oxygen,” Dreves said.

Fish need dissolved oxygen to survive, so the layer of the water below the thermocline becomes a dead zone as the air temperatures rise. Lures or bait presented there is the same as casting into a desert.

“The further you go into summer, the more the thermocline matters,” Dreves said. “It varies from year to year how long it takes for it to set up.”

Anglers want to target the area just above the thermocline for the best summer fishing. “You have that happy medium of the coolest water with good dissolved oxygen,” Dreves said. “You might find baitfish at that level as well. That zone will be the active part of the food chain.”


The fertility of the lake determines the location of the thermocline. Water clarity is a good indicator of fertility; murky lakes contain more nutrients in the water than lakes where you can see the bottom in 12 feet of water.

On a highly fertile lake such as Taylorsville, the thermocline starts at about 8 feet deep in mid-summer and ends at roughly 12 feet. Bass anglers fishing a heavy jig 18 feet deep on a channel drop are wasting their time, the same as anglers dunking cut bait for channel cats at that depth. There is no dissolved oxygen that deep.

Anglers need to pound that water from 6 to 10 feet deep or so in the summer heat on Taylorsville for bass, crappie, catfish and even bluegill.


“On a clear, low fertility lake like Laurel River Lake or Lake Cumberland, the thermocline may start at 30 feet deep,” Dreves said. “On these lakes, there can be good dissolved oxygen below the thermocline. They have a two story fishery where cool water fish such as walleye or striped bass locate below the thermocline in summer.”

On mid-depth, moderately fertile lakes such as Nolin River Lake, Barren River Lake, Green River Lake or Rough River Lake, the thermocline usually starts around 11 to 12 feet deep in summer with little dissolved oxygen below 16 feet.

“Find banks, channel drops or humps at that depth and fish them,” Dreves said. “I always remind myself to fish the right depth in summer.”

The U.S. Army Corps of Engineers Louisville District webpage has charts showing the water temperature and depths of the dissolved oxygen at www.lrl.usace.army.mil. Click on the “Water Information” tab, then the “Lake Temperatures and Dissolved Oxygen Levels” tab.

The depth where the oxygen line takes a left toward the zero side of the graph is the top of the thermocline. “You can also go out in the middle of the lake and turn up the sensitivity on your sonar unit until you see a band in the depths,” Dreves said. “That band is the thermocline. It seems the older units might pick this band up better than the newer ones.”

Lakes with high flow through rates such as Kentucky Lake and Lake Barkley usually do not form thermoclines in summer in the main lake, but thermoclines may appear in their major creek arms or embayments. The current in rivers prevents thermoclines from forming.

Remember the role of the thermocline while fishing this summer. It will put more fish in hand.

Editor’s Note: Author Lee McClellan is a nationally award-winning associate editor for Kentucky Afield magazine, the official publication of the Kentucky Department of Fish and Wildlife Resources. He is a life-long hunter and angler, with a passion for smallmouth bass fishing.

Get Your Fish On.

Plan your next fishing and boating adventure here.

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Recommended Articles

See More Recommendations

Popular Videos

Hunting Elk with the Ruger Hawkeye Long Range Hunter in 6.5 PRC

Hunting Elk with the Ruger Hawkeye Long Range Hunter in 6.5 PRC

Michael Cassidy and Paul Pluff talk about their elk hunt in New Mexico using the Ruger Hawkeye Long Range Hunter.

Action and Power Ratings- How to Choose the Right Bass Rod

Action and Power Ratings- How to Choose the Right Bass Rod

Most fishing rods feature both an action and a power rating, but what do those ratings mean and how do you use them to select the right rod for different scenarios? In this video, outdoor writer and tackle specialist Shane Beilue breaks down the difference between a rod blank’s action and power and discusses what the various ratings of each mean.

Hobie MirageDrive 360 Kayak Propulsion: Amazing Control and Power

Hobie MirageDrive 360 Kayak Propulsion: Amazing Control and Power

The Hobie MirageDrive 360 pedal propulsion system is the pinnacle of kayak control with more efficient fin designs, glide technology and allows the boat to be moved in any direction.

Catch More Bass on a Jerkbait in the Cooler Months

Catch More Bass on a Jerkbait in the Cooler Months

This one simple trick will trigger more bass strikes on a jerkbait during the fall months.

See More Popular Videos

Trending Articles

Who needs live bait when the big 'gills are so eager to strike these lures?5 Great Lures For Bluegills Other Freshwater

5 Great Lures For Bluegills

Stephen D. Carpenteri - March 10, 2011

Who needs live bait when the big 'gills are so eager to strike these lures?

Get ready to braise ground venison with all the traditional chili ingredients, directly on the grill, for a smokin' hot take on this comfort food classic.Smoked Venison Chili Recipe Wild Game

Smoked Venison Chili Recipe

Eva Shockey - October 16, 2020

Get ready to braise ground venison with all the traditional chili ingredients, directly on the...

If you haven't looked at the smaller urban lakes in your area, you are missing out on some great bass pond fishing.Bass Pond Fishing: Catch Lunkers at Small Lakes Near You Bass

Bass Pond Fishing: Catch Lunkers at Small Lakes Near You

Dan Anderson

If you haven't looked at the smaller urban lakes in your area, you are missing out on some...

Want to test the outer limits of your shooting skill? You'll need a cartridge that lives up to the expectations demanded at ranges up to and beyond 500, 600 or even 1,000 yards. Try these different loads until you find the one that thumps steel at long ranges consistently.10 Best Long-Range Rifle Cartridges Ever Made Ammo

10 Best Long-Range Rifle Cartridges Ever Made

David Hart - January 14, 2015

Want to test the outer limits of your shooting skill? You'll need a cartridge that lives up to...

See More Trending Articles

More Bass

As bass retreat from summer's warm weather it's time for 'football season.'Football Jig: Go Deep for Summer Bass Bass

Football Jig: Go Deep for Summer Bass

Mike Pehanich - July 13, 2020

As bass retreat from summer's warm weather it's time for 'football season.'

Employ these expert tips for world-class smallmouth bass fishing in rivers and streams.Go With the Flow for August Bronzebacks Bass

Go With the Flow for August Bronzebacks

Ken Duke - August 13, 2020

Employ these expert tips for world-class smallmouth bass fishing in rivers and streams.

When it comes to lure selection for summer bass, most anglers don't think of crankbaits first. Here's why you should change that thinking.The Quintessential Guide to Summer Cranking for Bass Bass

The Quintessential Guide to Summer Cranking for Bass

Pete Anderson - August 13, 2020

When it comes to lure selection for summer bass, most anglers don't think of crankbaits first....

When reel speed is critical, you have lots of choices. Here are 3.Bass Blazers: The Right Gear for Speedy Retrieves Bass

Bass Blazers: The Right Gear for Speedy Retrieves

Ken Duke - August 25, 2020

When reel speed is critical, you have lots of choices. Here are 3.

See More Bass

Magazine Cover

GET THE MAGAZINE Subscribe & Save

Digital Now Included!

SUBSCRIBE NOW

Give a Gift   |   Subscriber Services

PREVIEW THIS MONTH'S ISSUE Arrow

Buy Digital Single Issues

Don't miss an issue.
Buy single digital issue for your phone or tablet.

Buy Single Digital Issue on the Game & Fish App

Other Magazines

Special Interest Magazines

See All Special Interest Magazines

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Phone Icon

Get Digital Access.

All Game & Fish subscribers now have digital access to their magazine content. This means you have the option to read your magazine on most popular phones and tablets.

To get started, click the link below to visit mymagnow.com and learn how to access your digital magazine.

Get Digital Access

Not a Subscriber?
Subscribe Now