Understanding the Fall Turnover Period

Understanding the Fall Turnover Period

As cold weather rolls in from the North, the surfaces of reservoirs and lakes cool, making their water heavy enough to sink and mix with cooler water in the thermocline below. Wind encourages the mixing, and eventually the thermocline narrows, then disappears. As cooled water from the surface sinks to the bottom, debris bubbles up to the surface, accompanied by hydrogen sulfide and other gases produced by disintegrating plants, releasing a musky or sulfurous smell.

Fishing gets difficult under such conditions, but fortunately, Turnover lasts only about a week on any one lake. Once the lake or reservoir has turned over, the fall Coldwater Period begins.

SUMMER: The upper (warmwater) layer may be from 12 to 40 feet thick, while the thermocline may be 2 to 15 feet thick. The lower (cold­water) level usually contains less dissolved oxygen than the upper layer.

//content.osgnetworks.tv/infisherman/content/photos/10-9-19_ART2.jpg
POSTSUMMER: The surface of the water radiates heat to the atmosphere at night as water above the thermocline gradually cools. The thermocline remains intact but becomes closer in temperature to the layer above. Oxygen-poor water remains trapped below the thermocline.

IMMINENT TURNOVER: The thermocline shrinks as it approaches the same temperature as the uniform mass of water above.

TURNOVER: The thermocline disintegrates, and water mixes from surface to bottom. The water continues to cool as it circulates, aided by wind. The oxygen level of the water drops for a short time as the oxygen-depleted hypolimnion mixes with the water above.

Recommended for You

Spring walleye fishing often means large numbers of fish concentrated in small areas. Walleye

Spring Walleye Fishing Tackle Choices

Steve Ryan - October 19, 2017

Spring walleye fishing often means large numbers of fish concentrated in small areas.

Catfish is meaty, juicy and holds up well in this soul-satisfying fried fish recipe with homemade chips and tartar sauce. Fish Recipes

Catfish Dinner with Homemade Chips and Tartar Sauce Recipe

Jenny Nguyen-Wheatley

Catfish is meaty, juicy and holds up well in this soul-satisfying fried fish recipe with...

Balance is the goal when tipping jigs with trailers. Bass

Rigging Soft Bass Baits Correctly

Matt Straw - May 15, 2018

Balance is the goal when tipping jigs with trailers.

See More Recommendations

Popular Videos

Abu Garcia Virtual Rod with Bluetooth

Abu Garcia Virtual Rod with Bluetooth

Pure Fishing's Andrew Wheeler tells Outdoor Sportsman Group writer Lynn Burkhead all about the brand new Abu Garcia Virtual rod that integrates Bluetooth technology through a free ANGLR smartphone app.

Minn Kota's Brad Henry shows OSG's Lynn Burkhead that there's much to like in the new Minn Kota Riptide Terrova saltwater trolling motor that comes with I-Pilot and an 87-inch shaft.

MLF BPT angler and former Classic champ Casey Ashley has been with Costa del Mar sunglasses his whole career. At ICAST 2019, he shows OSG writer Lynn Burkhead some new products and talks how to pick the right lens color for the water.

See more Popular Videos

Trending Stories


Spring is prime time for pike. The Prespawn and Postspawn periods offer excellent odds at catching Pike & Muskie

How To Catch Pike In Spring

Dan Johnson - April 26, 2016

Spring is prime time for pike. The Prespawn and Postspawn periods offer excellent odds at...

Catfish are simple creatures that can be caught using the best catfish rigs. Catching them is simply a matter of putting a good bait in the right in front of them. Catfish

The Best Catfish Rigs

In-Fisherman - January 11, 2018

Catfish are simple creatures that can be caught using the best catfish rigs. Catching them is...

Check out this Largemouth Bass Length To Weight Conversion Chart, a simple and accurate explanation from the In-Fisherman biologists. Bass

Largemouth Bass Length To Weight Conversion Chart

Dr. Rob Neumann - January 22, 2017

Check out this Largemouth Bass Length To Weight Conversion Chart, a simple and accurate...

See More Stories

More Critical Concepts

The causes of barotrauma are based on two important laws of physics. Critical Concepts

Barotrauma: It's All About Laws

Steve Quinn

The causes of barotrauma are based on two important laws of physics.

Here's some important information regarding holding trophy bass. Critical Concepts

Holding Bass the Right Way

Ralph Manns - September 12, 2019

Here's some important information regarding holding trophy bass.

Attaining a measure of efficiency in any given situation is a vital part of successful fishing. Critical Concepts

Balancing Tackle & Fish Talent

In-Fisherman - December 26, 2019

Attaining a measure of efficiency in any given situation is a vital part of successful...

See More Critical Concepts

GET THE MAGAZINE Subscribe & Save

Temporary Price Reduction

SUBSCRIBE NOW

Give a Gift   |   Subscriber Services

PREVIEW THIS MONTH'S ISSUE

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