Thermocline fishing?

[LBL]

Went fishing yesterday
Did some research beforehand. You can clearly see the thermocline on my fish finder. Apparently in the summer this acts as a barrier to the fish (oxygen depletion below). Chronomids will still hatch below. They and other food sources will get kinda trapped at the thermocline due to the difference in water density and fish will lay right on top and feed. If the sonar is not reading the thermocline it looks like the fish are just floating mid column.

It sure looks like I could see fish doing exactly this on my finder. The thermocline was clear and so were fish.
This was in 30-45 ft of water. I couldn’t anchor with my anchor rope set up. Too short.
Only fish I caught were by trolling in the areas described. Who knows what depth my fly was at. I tried the dangle but not being anchored I couldn’t hold position well enough to be confident in my depth.
It would be really interesting to look at this with a live scope sonar to see if what I saw was real.
I’m going to get 50-60 ft of rope before next time. The fish were suspended at about 25’

Anybody have any comments or experience with fishing the thermocline?

 

[Salmo_g]

There certainly is a temperature gradient in lakes. By diving into lakes I always noticed that the water was much cooler under the upper two feet of warmer water. I thought I learned that thermoclines tend to set up in the range of 50 to 56 feet of depth. I guess I thought that was sorta' universal, but I'm not really sure.

I did have the experience at a central WA lake where I only place I could get a bite was at 29'. I marked fish above and below that depth, but couldn't get a bite. My friend is a far more accomplished trout angler than I, and his conclusion is that there were chironomids hatching in a particular location that was about 29' deep. I dropped 'mids down 28' in that spot and began hooking one trout after another. I never thought about whether the water temperature was a factor in play.

 

[troutpocket]

I’ve been successful trying to target areas where the thermocline meets a muddy lake bottom. Sometimes fish concentrate and I have done well with chironomids, leeches, or aquatic nymphs under an indicator on a 30’ leader, dangling with a full sink line, or casting and stripping using a count down to estimate depth. About 30’ is my limit using a 60’ anchor line. I try to scope out the line to minimize fish wrapping up.

 

[Mike Cline]

Yes, but in a little different setting. While living in the South, I routinely fished a small reservoir that was pretty much river-run with only one major tributary arm. The reservoir was 7.5 miles long and its upper end directly below a 44,000 acre reservoir impounded by a 168 foot high dam. The downstream dam on this reservoir was 87 feet high. When the upstream dam was releasing water it was very cold. Mid summer when surface water temps might be in the high 80s, this cold water created an instant thermocline the length of the reservoir. We used to swim and snorkel a lot in this reservoir and about midway (3.25 miles) from the upstream dam the cold water was usually about 6 feet down. It was shocking to find yourself in 80 degree+ water at the top with your feet dangling in extremely cold water. At the upstream dam the water was essentially cold all the way to the surface with only backwaters and bankside waters having any warmth. As you moved downstream the surface waters warmed until the thermocline was very deep close to the downstream dam. The reservoir was chock full of hybrid striped bass, white bass, spotted bass, yellow perch, and very large bluegill and shellcracker. When the thermocline was in reach while snorkeling in the upper reaches of the reservoir we learned very quickly where the fish hang out—just above the thermocline, especially post spawn. So as we fished closer to the downstream dam we fished deeper and as we fished closer to the upstream dam we made more shallow presentations.

 

[RCF]

Last decade my wife and I were King County volunteer lake stewards of the lake we live on. Every 2 weeks we would take water quality samples, water temps , and water visibility at specified levels. We did the monitoring 7 months a year for about 5 years. The lake is 50' deep. There are 2 distinct thermoclines: one around 20' deep @ ~55 degrees and one around 40' deep @ 45 degrees. They were always there and did not change by time of year nor year by year. The fish hung around the 20' mark quite consistently.