When Does Fall Turnover Occur ?

[scaleface]

I live in Northern Missouri .Theres a 200 acre lake that I fish often . It has a maximum depth of 30 foot  All summer I could plainly see the thermocline on the sonar . Early in the summer it was unusually shallow with the top of  it at around ten foot  , by late summer the top of the band was around 17 foot with a surface temperature in the   80's and 90's.  Last week  I visited the lake for the first time in more than a month . I could see no visible thermocline on the sonar and the surface temp was 72 . I concluded that the lake had turned and posted it here. Another member thought it  was too early for my location and he is probably correct . 

 

Heres my questions .

 

Can one tell if a lake has turned over if the themocline is no longer visible ?

Could the thermocline itself have dropped deeper and was now not visible because of the relatively shallow lake ?

What should the surface temp be for the lake to turn ?

[lo n slo]

I read that. You did seem to have the thermocline dialed in for most of the summer. You also noticed a change. Surface water temps dropped significantly. Visible thermocline no longer present on your graph. I truly think some "mixing" has begun to take place. Maybe not a full fledged turnover, but things are changing for sure.

My fishing experience, around here, with the turnover, is brownish water color and a noticible odor. Some bottom debris floating on the surface and the bite is all but shut down for a couple weeks. Wind blown banks and pockets seem to accumulate more oxygenated water but the bite is still way off.

I am a retired Operations Supervisor in the Drinking Water Treatment Industry and my professional experience with the turnover is one of taste and odor related water quality issues, as well as, high raw water turbidity issues. Some years it would arrive sooner than later, usually sometime in mid/late October to early November. Maybe a call to your local water authority could help you fine tune your understanding? Anyway's, sorry for rambling and I do enjoy reading your posts.

[WRB]

Turn over can be caused by high wind mixing a shallower lake, however shorter day time heat and longer night time colder temperature is the primary cause. Thermocline depth changes constantly, it's not a static layer.

If you don't meter a sudden change in water temps indicating the thermocline, the baitfish and bass are at various depths, the lake more than likely turned over during the time you were away. The bottom debris and sulfur like smell settles down in a few days, the water column equalizes in a week or so.

There isn't a calendar time period for weather, the suns location is what our calendar is based on, fall occurs when the sun is directly over the equator, fall equinox happens today.

Tom

[Wayne P.]

You can have a somewhat cool surface temp and the thermocline will still be present.

 

This is a cool fall morning, note the surface temp, yet the thermocline is very distinct. All the mixing to equalize the water temp has not occurred. It can take as long as a few weeks for the turnover if no warming trend occurs.

 

 

[Wayne P.]

Kind of in between the above and below:

 

 

 

 

Summer:

 

[lo n slo]

Good stuff Wayne

[Team9nine]

 

 

Heres my questions .

 

Can one tell if a lake has turned over if the themocline is no longer visible ?

Could the thermocline itself have dropped deeper and was now not visible because of the relatively shallow lake ?

What should the surface temp be for the lake to turn ?

 

One way to judge if the thermocline is still present is by how deep you are marking fish on your depthfinder. Once the thermocline is completely gone, fish have the option of using the entire water column, and some fish will. When you start graphing fish along the bottom in the deepest water, you can generally assume the lake has completed turnover. 

 

As surface waters cool and start mixing with the deeper waters, the thermocline drops deeper and deeper until it eventually is completely removed. It wouldn't be unusual to also have a weaker temperature gradient and somewhat more disbursed organic matter, thereby making the thermocline not quite as distinct on some units as in the peak of late summer.

 

The actual surface temperature will vary from lake to lake depending upon what the temperature of the anoxic zone underneath the thermocline was. Water depth and lake type can play a role in determining this. However, a general guideline on my local reservoirs (Indiana) is that when surface temps are in the mid to low 50s, the lake is usually pretty close to having completed turnover.

 

-T9

[scaleface]

Good info everyone . So I'm guessing that the lake I was referring to was in the process of turning over .

[Catt]

It can take as long as a few weeks for the turnover if no warming trend occurs.

Like I've said may times before "think of it as pre-spawn but in reverse".

[MDBowHunter]

Its happening right now where I fish, yesterday was my worst outing all year.

[scaleface]

Theres been times when the sonar would show a lot of clutter off the bottom , sometimes in a wide band . I'm speculating this would be the water mixing and bottom debris suspended ?  Am I wrong or correct  ?

[hoosierbass07]

 I don't know if the clear water strip pits I fish on with my kayak are changing over now or not but last week the water felt warm to my hand, warm enough to swim in.  Sunday evening I went to another strip pit close by and noticed the water is a on the cool side, too cool to shower in or shave with.  So they are changing here in west central Indian.  Also  noticed some gunk floating on the surface.  

[lo n slo]

Went out yesterday. It has been cloudy, rainy and cool, with steady NE winds, for the last week, here in the western piedmont of NC. Surface water temp has dropped a good 7 degrees in that span...we've dropped from 83 to 70 in the last two/two and a half weeks here. I did notice some brown water where it has been clear. Dont think that the entire body of water has turned but things are heading that way IMO. I did manage to catch some shallow fish on the Red Eye. Had the lake to myself too. More rain today but Imma try to sneak off to the lake if I get a window.