Water temp under the ice & Fish feeding activity

[Jim F]

Does anyone have a idea as to what  temperatures are under the ice? (not surface temp)
I know you cant tell me what it is 50 feet down in Lake Whatever in NW Montana.
What I'm getting at, is- does the entire lake cool down significantly (and somewhat uniformaly)
 or is the temp likely to stay higher in deeper water? Is it worth the expense to get a
thermometer that will read at depth, and start looking for more ideal temp zones for fish?
If so, can you recommend a thermometer that will read remotely, so you get accurate
readings at depth, rather than changing as you raise it to the surface.

In summer time, we all know that deep water is cooler than surface water.
 Is the inverse true in winter?

Insight appreciated

[Swift]

Water is at its most dense @ 39.2*F. I'd look more for oxygen levels in winter, doesn't matter what the temp is, no air - no fish

[ClearCreek]

Like Swift said water is most dense at 39.2F (4C) so in a lake covered with ice the water just under the ice is 32.1F and as you progress deeper the water gets "warmer" and on the bottom of the lake it will be 39.2F. 

Now, a stream running into a lake can change things depending on the size of the lake and stream contributing water to the lake/reservoir.

ClearCreek

[Jim F]

So what you're saying is there isnt likely to be any water warmer than 39.7 degrees in the winter,
with the exception of maybe near a stream inflow.

[Lobes]

Water near an inlet would likely be colder. My camera reads water temperature and it typically reads 36 - 38 degrees. I'm not sure how closely it's calibrated but I'd think it's within a couple degrees.

                                       
NBG

[eriksat1]

I guess if it got any warmer it would rise, then cool off again near the top. Like was said oxygen is more important, and the deep water sometimes losses more oxygen than near the surface. Low oxygen really puts the fish in a dormant stage almost to the point of a hibernation.

[Ramp 23]

The lake I mainly fish is spring fed. Useing a "Cline finder " I can locate springs which are 52 deg. Mainly from summer fishing ,GPS ing the spots with the clin-finder. In july / august it`s helpful . In winter it , in my experience, hasn`t helped ice any fish. I think it rapidly rises & cools .  I have found spots that did hold at 43 though.  I agree with other posts oxygen is more an issue in winter.