I was wondering if anyone could share more info about Thermocline. I grew up in Arkansas and there was really no thermocline in the lakes there. I know live in the Minnesota and want to learn more.

I was wondering ...
1. If any had more info about thermocline and how it work here in BWCA?
2. What fish species are effected by it?
3. Do you need to fish below it or right at it for bigger fish and lakers?

-CanoeViking

If you have a depth finder most of the time you can see the thermocline on the graph. It is a definite change in temperature in a lake. The fish in spring will be above the thermocline because that’s where the oxygen is. You can find fish below the thermocline, depends on the tone of year. All fish are affected by it. It varies throughout the year if the fish are above or below. I use my sonar to find this out. Then there is the turnover, where the cold and warm water mix. This happens in the fall and spring when the water is warming or cooling.

A Thermocline is the layer of water where temperature drops rapidly. Because water is the densest at 39F, turnover happens when the surface water cools to 39F, sinks, and displaces the oxygen poor bottom layer (hypolimnion). Primer.

The main Fall turnover occurs when the surface temp cools to the low 60's. A secondary less dramatic turnover can occur when the surface temp warms to 39.

In much of Minnesota by mid summer on lakes in north central Minnesota water below the thermocline(a thermocline starts where you have about 0.6 degree F. drop per vertical foot of water) is often devoid of oxygen because of dying algae and weeds utilizing and using up the oxygen. Many BWCA lakes because of deep water and also more infertile water(less vegetation etc.) will have good oxygen supply to the bottom. Especially lakes with lake trout.

Thanks for the info. I understand more how it works now.

So my question do fish prefer the top of bottom of the thermocline?

quote CanoeViking: "Thanks for the info. I understand more how it works now.


So my question do fish prefer the top of bottom of the thermocline?"

Top of the thermocline is way more productive, fish look up and look for the shadow of their prey against the light. I'd say the thermocline is mostly between 30 and 45 feet in bwca lakes, one time in August on Lac La Croix we were killing the Lakers we found next to a near-70 degree underwater cliff, going down maybe 60 feet, with 1oz jigs with 3" white plastic worms. Drop it DEEP then reel it up as fast as possible, and don't let them rip the rod out of ur hand!!! :P. I don't think they could help their predatory instinct seeing that jig scream for the surface.

Top of the thermocline is way more productive, fish look up and look for the shadow of their prey against the light. I'd say the thermocline is mostly between 30 and 45 feet in bwca lakes, one time in August on Lac La Croix we were killing the Lakers we found next to a near-70 degree underwater cliff, going down maybe 60 feet, with 1oz jigs with 3" white plastic worms. Drop it DEEP then reel it up as fast as possible, and don't let them rip the rod out of ur hand!!! :P. I don't think they could help their predatory instinct seeing that jig scream for the surface. "

That’s what I thought. That does sounds like a fun day!

Larger lakes the thermocline will be deeper due to wave action circulating top water. Where fish our in the thermocline depends on time of year and water temps. Also in smaller panfish lakes in August in mid Minnesota there probably won't be any oxygen below the thermocline.
BWCA lakes often have oxygen to the bottom.
Also which fish Species you seek it makes a difference. Walleye prefer like aprox. 65 degrees,lake trout in the 50's. Also all depends where the forage fish hang out.

Any suggestions or tips on judging the water temp between the thermocline and the surface temp?

quote CanoeViking: "Any suggestions or tips on judging the water temp between the thermocline and the surface temp?"

Sometimes on a medium size lake in August the first 20 feet will be like 75 degrees F.. As summer goes along the top of the thermocline gets depressed-meaning once the temperature starts changing it could change fast. Each lake and lake types vary so much.

Thanks again for the helpful info.

quote Savage Voyageur: "If you have a depth finder most of the time you can see the thermocline on the graph. It is a definite change in temperature in a lake. The fish in spring will be above the thermocline because that’s where the oxygen is. You can find fish below the thermocline, depends on the tone of year. All fish are affected by it. It varies throughout the year if the fish are above or below. I use my sonar to find this out. Then there is the turnover, where the cold and warm water mix. This happens in the fall and spring when the water is warming or cooling. "

Very well said, in the summer this is the magic zone...