Thermocline on the river

Has any one ever dropped there AquaVue to the bottom of the river in over 50 fow, the AquaVue with the temperature sensor that is? I’ve read that the river doesn’t have a thermocline, and I understand water flow and rivers, but I’m curious about what people have found. Has anyone found a distinct temperture differnce that would indicate a theromcline? Also please indicate what time of year you have dropped the camera into the deep.

Keep catchin’
Turk

Tossing and turning over this burning question last night???

When I go swimming its much colder a 4-6 feet under just like a lake. I would sure guess a deep river has a thermocline.

Turk,

I might be wrong, but with moving water in the river(even very slow current), I dont think it would be able to get a significant thermocline. The most significant temperture change will likely be a few feet below the surface on a hot sunny day where the heated surface water mends(for lack of proper word) with the water that is not as heated by the sun.

Rivers have always confused me some, but there is some temp variation over the depths in minimal current situations in deep water, but not as much as lakes. It doesnt make sense to me why the water isnt the same temp from top to bottom, the water constantly moving one would think would always be mixing it up??

Turk, I saw a presentation last fall that indicated Lake St. Croix has a summer thermocline. I can’t remember when or where the observations were made, but it seems the thermocline was relatively shallow (maybe at 15′). In addition, it had notable DO sags below the thermocline.

I can’t find the study posted on-line, but I believe the work was done by USGS and/or the St. Croix Research Station.

Rivers don’t normally stratify, but Lake St. Croix is a different beast. I’m guessing the observations may have been made in the deeper parts of the river (south of Hudson), but thats only a guess.

You may find this response elsewhwere on the web…

the only time I have found a large temp change is when I have found a spring
the water there is colder and forms a pocket or bubble for lack of a better term that rides the bottom down current and slowly mixes with the warmer water
I have found some in slower current that were
several yards wide and up to 50 -100yds long
big pike love them
not many old timers will give up these spots as they are always good I have found some on my own and was shown a few by a old river rat that I shared my boat with many years ago
he’s gone now but the spots are still there and so are the pike

Nice replys guys, good stuff to think about. Ya, I’d like to see that study as well.

I used to have a german made depth and temp sensor, Cabela’s sold it. You threw it out and let it sink, then haul it back in and click a button to get a reading of the temperature for every five feet of water.

I did this near Hudson deep water and in the Bayport pool, this was in mid July if I remember correctly. I found an eight degree difference, and no severe change from any depth range. This is why I believe it has no thermocline.

I was hoping someone with the camera and temp sensor did the same “experiment” and was curious if the results were similar.

I’d really like to crack the Late July/August walleye bite and I think the open water has everything to do with their location. So I was wondering if I had to mix thermocline in with my plan…

Thanks boys!
Turk

Hey Turk, Excellent question! I’ve often wondered about them and how fish relate to them not just on the Croix.

Please do a temp check just down river from Catfish where it gets really deep! I seem to remember seeing one there and also down in Afton where it is really deep using my depthfinder in the past. I find it hard to believe there wouldn’t be one with the >70 degree average surface temp on the Croix from June thru August in the DEEP slow water areas of the river.

Remember colder water is more dense (39 degrees densest) and will cause a different return on the depthfinder if you have the gain up. I’m not sure how that relates to actual water temp since I just measure surface?

On a related note I know of a place on the Ottertail river in 40′ of water where there is almost always a darker return 20′ down (thermocline?)Acording to In-Fisherman of long ago there are NEVER fish below it??? I question that theory when reading of salmon and trout fisherman fishing above and below it? How about the flatheads on the Croix?

Later,

Ferny