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PoconoTom

Does Surface Temperature Tell You Underwater Temperature?

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If you know the surface temperature of a lake, is that close to the underwater temperature?

I have a non-submersible thermometer, but was wondering if the effect of the sun or whatever on the surface would make that reading inaccurate for even the first say 6' of depth or so.     

I'm mainly interested in the top 5'-6 feet.     I know there is a thermocline down there somewhere where things change.

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Have you ever swam in a lake? If you have you should know deeper water is colder than surface water during the summer.

Every lake is a little different regarding water temperatures from surface to various depths depending on the size and depth of the lake, it's regional location, wind and day/night air temperatures. 

It's summer almost everywhere including PA. Lakes are different then rivers because of current that mixes the river water verses very little current in most lakes.

During the summer the lakes surface water warms every day and cools somewhat every night. Early morning the surface water is about the same as the water 2' to 4' down on the main lake basin, warmer in shallow bays. The coldest water will be located at the thermocline depth that varies with each lake, somewhere around 15' to 30' on average and about 5 to 10 degrees colder than surface water temps. 

Tom

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I could go into a long explanation on Thermocline and Stratification and Gradients, but there are soooooo many factors that play into the answer it would be extensive and without knowing the body of water, clarity, bottom composition, location, etc., it would not be relevant so.......the short answer is yes, the deeper you go the colder it gets with the exception of the fall when most lakes "turn-over".   

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As already mentioned, there are a lot of variables involved. However, once you reach the more stable summer environment, and since you are only interested in the top 5-6 feet, it is probably a safe generality to say the temp reading across that small of depth range will be fairly consistent (similar to surface).

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The experts have spoken. I'll just welcome you to the

forums!

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Bass Pro use to sell a temperature/ light meter with a probe on a long cable . I used it a lot and it was a valuable tool for me . The answer is no . The temp drops the deeper it gets . Right at the thermocline [if there is one] the temp and the light drops at a much greater curve . It was so predictable that i quit using it when there was a thermocline present  .  

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Here's a screenshot of the water profile of one of my local reservoirs that the COE provides. This was just captured last week. What you'll see is the water volume above the thermocline, everything from the surface down to 20' in depth, is all within 1 degree F in temp. This upper layer of water, known as the epilimnion, stays separated from the lower, colder waters by the thermocline. As such, it tends to stay well mixed and is usually very consistent in temperature once surface heating is well underway. Things will by and large tend to stay this way all the way until cooler fall weather. The thermocline right now runs from 20' down to 30' where the water temp then once again stabilizes.

 

IMG_1059.thumb.PNG.b320110eb5de319dccd4f9e2dcb3cfa4.PNG

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Lots of great information in those previous posts, and under normal conditions,  in most bodies of water, very true. The exception to what was said is underwater springs that produce a constant stream of water at the same temps all year long.  These spots can be magical in winter when surface temps drop way down into the 40's in Florida and all forms of aquatic life seek these warmer waters.  In summer when it is unbearably hot, and water temps get into the 90's, these deep springs supply a relief from the heat at a constant 72*.  Because of the flow and current O2 levels are also good.  The everglades has several spots with springs in the canals, that are famous for stable catch rates during some of the most difficult times, during these extremes in temperature.  Subsurface temps are key to finding these areas.  Just another use for this type of tool.

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Some lakes do not have a thermocline because they are not deep enough so the surface temperature is likely pretty close to the temperature in 20 feet of water.  Water clarity plays a big role because sunlight penetrates deeper and warms up the water quicker if its clear versus being murky.  Also, volume of water is a factor too.  Think of trying to heat up a small cup of water versus a tub.  It takes a lot more energy and time to heat up the tub than a cup.

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Thanks for the informative comments.

I decided to take some of the guesswork out of it, and I ordered one of these underwater thermometers.      They tout it as a stream and river thermometer.    I guess the trout fishermen are interested in getting more accurate temperatures than the bass fisherman are concerned with.

https://www.amazon.com/gp/product/B00BSFZTOS/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

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