What causes a lake to turn over?

[jazzwannabe]

And what happens when it does?

[kopper_bass]

simple thermo-dynamics
Cold water sinks because its more dense and heavy, Warm water rises because its lighter and less dense.

As the air temps outside get colder, it cools the water on the top layers. this water becomes heavier and denser than the water (and heat) trapped at the bottom of the lake. Soon enough, they reach a point of conversion and flip. The warm water rises up to the top of the lake and the top, cold layer sinks to the bottom.

The fish and bait tend to go to the top layers at this time with the warmer water. it has nutrients it pulled from the bottom of the lake, along with alot of oxygen. soon after though, the lake settles into an equilibrium until the top layer once again gets colder and heavier than the bottom layer and the process continues. At some point though, the bottom layer gets so cold that the top layer never goes beyond that temp and it equalizes to stay at this level thru the spring, summer and fall. Only during the summer does the bottom layer warm enough to be displaced the next winter with cold water.

Hope that explains it for you.

Kopper_Bass

[jazzwannabe]

Thanks, Kopper.

[BassManDan]

Good answer Kopper, a limnologist couldn't have said it better.

[Oldschool]

A detailed explanation can be Googled; "weather elements:fall/spring lake turnover, the weather doctor.
Most of our bass lakes do not freeze over, so look at the summer and fall conditions.
The type of turnover that kills fish, ie; Canyon lake, is dissolved oxygen depletion caused by bottom decayed debris consumming DO when it becomes suspended or rises, when the lake turnsover, combined with the mix of cold low DO hypolimnion water layer. The fish get a combination of thermal shock and low DO.
Normally wind tends to add DO by wave action and our mild cold nights slowly cools the water surface and gradual mix of the water column occurs.
Tom

[Oldschool]

Here is the link for those who may be interested.
http://www.islandnet.com/~see/weather/e ... nlakes.htm
Tom

[TonyL]

Man , Oldschool reminds me of Tim The Tool Man's neigbor !

[RogerB]

Thanks, Oldschool! That's a very clear explanation of the fall turnover.

As an example of a turnover, my son and I fished Lake Chabot last weekend. Using a Lowrance temperature gauge, I determined that the thermocline began at 33 feet (identified by a rapid drop in temperature as the probe is lowered). Since the thermocline is usually a narrow band, the likelihood is that the virtual "bottom of the lake" was somewhere around 38-40 feet, even in those areas of the lake where the actual depth exceeds 50 feet.

As explained in your referenced article, there is usually insufficent dissolved oxygen below the thermocline to support fish life. Hence, the bottom of the thermocline represents the virtual "bottom of the lake" and it's a waste of time to fish below the thermocline.

[Steve]

THence, the bottom of the thermocline represents the virtual "bottom of the lake" and it's a waste of time to fish below the thermocline.

Not necessarily. Depends on the trophic category of a lake. That would apply to highly fertile, eurtophic lakes. However, infertile oligotrophic lakes have plenty of DO below the thermocline. Thats why you can catch bass in 120 foot of water in the summer at places like Orroville and Shasta.

[B.Cline]

Mother Nature