??? for Duck Soup/canvasbackca.


Well-Known Member
Dont pretend to be very smart on stuff like this so ask people who know:

How much typically does water cool with depth.

Just looked at a chart for Erie off Port Stanley and surface temps are now in the mid 60's (68-69) yet when at Bruce last week fish caught off the pier in 7-8' fow seemed quite cold to the touch.


Hi Packrat...I'm not sure you can chart temperature drop by the foot but Icefisherman has a probe on his downrigger that measures temp and electronically transmits the data to a screen in the boat. When we fished Lake Ontario the surface temp was pretty cool at about 60 degrees and the temperature didn't change much until 30 feet. By 45 feet it was only 39 degree F.
As I recall from my probe readings last weekend about 12 miles off Burwell, the surface temp was about 68 degrees, 64 degrees at 34 feet, and only 46 degrees just 2 feet below that. This distinct split is the "thermocline" where the cold dense bottom water separates from the surface water. The upper water continues to turn and mix and heat up all summer which entrains oxygen. The thermocline continues to go deeper and deeper as summer progresses.

The way I understand it is that there is very little oxygen in the bottom water. This in addition to the warmer temps is why the fish tend to hang out at or above the thermocline when they are actively feeding. That is the way it was explained to me but I'm sure there are differing theories on how this all works. I know for a fact though that fishing below the thermocline is not very productive for the most part.
I would rely on reports of actual water temp from our boys. Check out this note from the website home page. The temps given are only estimates.

NOTICE (3/10/2011): The Great Lakes surface water temperature estimates presented in this website are automatically generated from satellite-derived sensors. Obvious errors or anomalies may be present in the resulting images as a result of satellite sensor malfunctions, adverse atmospheric conditions, or processing errors. Please notify us immediately about any errors or anomalies you observe in our products. Send your questions or concerns to cwatch@msu.edu.
Sorry for the tardy response, Packrat -- been busy fishin' with a couple of friends from Alberta. We did Long Point smallies and perch, Port Bruce 'eyes and bows, an Erie trib for Browns, St. Clair muskies, and Deer Creek for largies, crappies, and gills. Their conclusion is that there's no other place in Canada that has the diversity and quality of fishing as does southwestern ON and I think that they are right!

Anyway, there's no one answer to how much water cools with depth because a lot depends on the size / shape of the lake basin and current and past weather conditions. But, there's little change with depth in the epilimnion ( volume of water above the thermocline ), a rapid decrease with depth in the thermocline, and then little change in the hypolimnion ( volume of water below the thermocline ).

This website does a good job of explaining that phenomenon:

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