Saturday I attended a lecture at Harry Murrays’ fine fly shop on brookie fishing in the Shenandoah National park. Very informative. He said he checked water temps and when a certain threshold was reached in the early spring he knew it was time to switch from nymphs to drys. I never paid much attention to temps, but I was so impressed I bought a thermometer for my pack! Anyway, I started wondering what else temps could tell us and found this: http://thefrogwater.com/2014/01/22/the-importance-of-water-temperatures-when-trout-fishing/
Some interesting items on this list - 50’ threshold for crawfish activity
- 42’ threshold for optimal midge hatch
- 40-54 for BWO
- 60’ threshold for damsels
Anybody else out there carry a thermometer and what info does it tell you?
Pillcaster,
It is always in my vest or sling pack. I rely more on it for trout activity than bug/prey activity. If the water is below about 45 degrees I will spend more of my time fishing the seem waters or in tail outs where they can hold with out much energy output. once the water begins to approach 50 deg. I will start to fish more in the riffle /run waters. one big reason to have it is to know exactly when the water has gotten over 68 degrees and time to head to the local tailwater. actual bug activity can be regional as well. I know here in CT we will have midges on the water when the water temp is 39 degrees. Rarely will the trout be rising to them on the freestones but you can get some good surface action on the tailwater then as well. In my 40 years of fly fishing I have found the best way to figure out what is hatching is to shake the trees/brush , seine the water to see what is there.
steve
Winter steelheading, a two degree rise in temp could mean a much more active fish willing to bite. Below 42 degrees, the colder the water the slower the presentation and also the slower the water the fish are likely to be holding in. Water temps give a little indication of when the spawning migration may start, although there are more factors that drive anything that I have just mentioned than only temps.
During the winter, I do a lot of nymphing, doesn’t matter what the water temperature is on the river, 30 degree water, 20 degree air, the fish will still be feeding, you just have to work the seams and ledges really good. But, I always keep a dry fly rod ready. Often the BWO hatches occur, more often than not the fish don’t pick up on them, but they are feeding on them as they rise to the surface. But, we do have some stonefly hatches occur during the late winter and the fish will key in on the females who are laying their eggs. Even during the spring & summer & fall, I will still be nymphing until a hatch comes off that the fish key in on, then the dry fly rod takes over again. I guess what I am saying is I don’t pay as much attention to the water temp as I do what the bugs are doing and how the fish are responding to them.
Larry —sagefisher—
The late JC and me did some basic research with stream thermometers back in the 60’s and early 70’s on Michigan’s AuSable River. We never came to any definitive conclusions based on water temperatures but research does show water temperatures do drive hatches and fish activity. The exact correlation between temperature and trout and hatch activity is also linked to the habitat. In streams where water temperatures are relatively constant, like spring creeks and tail water fisheries, hatches and trout activity are much more difficult to correlate with water temperatures.
Although I have not done a lot of checking for this, one good use of a thermometer is to find springs. This is best done either in the winter or the summer, when the temperature difference between spring water and surface water is the greatest. The locations of these springs will be refuges for fish when the water elsewhere either gets too warm or too cold, depending on the season.
I also carry a thermometer. Although rather than buying a “stream thermometer”, I’d suggest getting an inexpensive, instant read cooking thermometer similar to http://www.amazon.com/Thermometer-Electronic-Collapsibl-Replacement-Guarantee/dp/B011BF25HS/ref=sr_1_18?s=home-garden&ie=UTF8&qid=1453217930&sr=1-18&keywords=cooking+thermometer.
I use my thermometer year round. In the winter and early spring, it’s helpful for determining whether the stream is wamring up – sometimes a couple degree stream temp increase will trigger feeding. It’s also helpful to find warmer water locations such as near springs.
In the summer, it’s useful to know when streams are getting too warm. The usual wisdom is that as stream temps get to 68 degrees or so, it’s too warm to fish – fish aren’t as active and can be over stressed. With a stream thermometer, I can find cooler water – near springs or in a smaller tributary – or just decide to go home.
It’s also useful for determining hatch times. As you noted, BWOs generally hatch at 45 degrees or better. In my area, Dark Hendricksons hatch at about 50 degrees, Light Hendricksons at about 58 degrees, and trico spinner falls generally happen at 68 degrees air temp.
You can also combine these uses. So for example, when most of the streams are running low 40s in spring, I might seek out and a smaller, mroe spring feed stream that is running a little warmer and has an earlier BWO hatch.
I use a thermometer strictly for determining when the water is too warm to target trout.
I even carry one on a long string in my glove box for those days when I pass over a likely looking spot so I can lower it off a bridge to check BEFORE I get down to the water. If it is too warm, I move on.
As far as using one to determine hatch times or anything else related to fish behavior, I never met an insect or fish who carried one so I’ll stick to my eyes for determining when a hatch is happening and I’m not about to go home if the water temp tells me the fishing will be slow.
I’m dumb that way, I just wait to see what happens and chalk up lackluster results to incompetence but then again, I don’t base my fishing sessions on solunar tables either.
[b]okflyfisher[/b]
Senior Member 
Join DateMay 2004LocationOklahoma City, OK, USAPosts888
[IMG]http://www.flyanglersonline.com/bb/images/icons/icon1.png[/IMG] All my "home" waters are tail waters and everything is messed up. The rainbow trout even spawn in the fall