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The Dog Days of Summer and the Deep Freeze of Winter:

How ambient water temprature affects fish feeding behaviour






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     If you happen to live in one of those magical places where the water temperature is just right year round, then you probably enjoy excellent Trout fishing year round as well! However, if you are like most of the rest of us, then you too have to deal with the "dog days" of summer and the deep freeze of winter. In fact, even on small, heavily shaded, streams that run through deep gorges here in the Blue Ridge Mountains, I have actually seen schools of wild trout suspended in the water column at the tail of a pool that were so intent on obtaining enough oxygen to continue breathing that they completely ignored my presence standing over them so close that I could have scooped them out of the water with my hand! Needless to say that they were also far too intent on breathing to take any type of fly regardless of pattern or its proximity to their noses! On the other hand, the deep freeze of winter causes a similar problem because, as the water temperature drops, so does a Trout's metabolic rate and thus, their need for food also drastically diminishes. However, as long as you understand the underlying causes of poor trout fishing here in the South during both the dog days of summer and the deep freeze of winter, then you can adjust your tactics accordingly in order to improve your odds of catching fish.


    So, first let's talk about how to catch Trout here in the South during the height of summer. Of course, the problem with trout fishing in the South in the summer months is one of rising water temperatures which, in turn, adversely affects the availability of dissolved oxygen in the water. Now, the reason that this is a problem is that, contrary to popular belief, a trout's gills are not designed to break the Hydrogen/Oxygen bond of the water molecule in order to extract the Oxygen they need from the water. Instead, they are designed extract free roaming Oxygen atoms suspended in the water column called "dissolved oxygen" that are not attached to a Hydrogen atom. Also, Dissolved Oxygen becomes trapped in the water via the action of waterfalls, rapids, and riffles which churn the water and rain that injects it directly but, it should also be noted that the warmer the ambient water temperature is, the less Dissolved Oxygen it can hold and, the colder the ambient water temperature is, the more Dissolved Oxygen the water can hold.  Therefore, it has always struck me as God's little joke on both Man and Trout that, because a Trout's metabolic rate is determined by the ambient water temperature and is at its highest in warmer temperatures and at its lowest at colder temperatures, their metabolism is at its peak when the availability of Dissolved Oxygen is at its lowest and, when the availability of Dissolved Oxygen is at its highest, their metabolic rate is at its lowest. But, of greatest importance to fly fishermen here in the South is the knowledge that trout will seldom feed in water temperatures above 65 degrees and, by 70 degrees, they are gasping for breath. So, in order to find populations of Trout here in the South who are willing to feed during the summer months, the trick is to find a stream with a water temperature below 65 degrees. However, this can be a tall order with ambient air temperatures sometimes reaching as much as 100 degrees in the lower section of the foothills and even the higher elevations hovering in the mid eighties on some days. So, in order to find a trout stream with a water temperature below 65 degrees during the summer months here in the South, you need three factors to come together in the same place and they are: springs, shade, and elevation. Now, the reason that inflowing springs are important is that because their water springs forth from under the mountains, it is significantly cooler than that already in the stream and thus, inflowing springs (called "branches" here in the South) lower the ambient water temperature of a small stream during the summer months and, of course, the more springs, the cooler the water will be. Naturally, shade is also an important factor because we are all aware that any object left in the Sun for a length of time absorbs heat and thus, direct sunlight on the surface of the water in a trout stream will significantly raise the ambient water temperature. Therefore, by searching out heavily shaded streams in the summer months such as those that flow through deep gorges and/or dense overhanging foliage, fly anglers are far more likely find populations of Trout that are willing to feed. Last, a third determining factor of fly fishing quality here in the South during the summer months is the elevation of the stream you are fishing. Now, this might sound like an oxymoron since we are already talking about fly fishing in the mountains but, because the Appalachian Mountain chain is far older than the Rockies, it is not nearly as tall and yet, it still serves as the Eastern Continental Divide. Therefore, most of the trout streams here in the southern Appalachians are located on either the western or eastern faces of the mountain slopes and thus, very few are actually located in the peaks of the mountains. But, those streams that are located at peak elevations are far more productive during the summer months than those located at lower elevations.


     Now, let's examine how to catch trout here in the South during the height of winter. As I mentioned previously, ambient water temperature is the controlling factor of the speed of a Trout's metabolic rate and thus, when the water temperature is low, so is a Trout's metabolic rate. Unfortunately for us fly fishermen, when their metabolic rate is slow, they also have little to no interest in feeding; just like when the water temperature is too high. In fact, it has been my experience that Trout in small streams here in the South will seldom feed in water temperatures below 45 degrees. So, what's a fellow to do? Well, the answer to that is to do the same thing that you would do in summer by looking for streams with inflowing springs. Now, I am aware that I said that inflowing springs lower the water temperature but, that is in the summer months. During the winter, the water that springs forth from the mountains is actually warmer than that in the streams and thus, you will often find populations of Trout in small streams that are willing to feed for as much as 100 yards downstream of a spring during the winter months! However, unlike during the summer months, another trick to finding populations of Trout that are willing to feed is to look for streams that are wide and/or have very little shade. That way, the Sun's radiation can reach the surface of the water and thus cause it warm and, during the winter months, a mere two or three degree rise in ambient water temperature can drastically increase the Trout's willingness to feed. Last, elevation is also a determining factor when Trout fishing in the winter here in the South as well. However, when fishing in winter, you want to search out streams located at lower elevations instead of higher ones because the ambient air temperature at the base of the mountains can often be fifteen degrees warmer than that at peak elevations. Thus, by searching out streams located at lower elevations during the winter months, you will find both warmer ambient water temperatures as well as populations of Trout that are far more willing to feed.


     So, when it comes to fly fishing during the dog days of summer or the deep freeze of winter here in the South, it is important to remember that Trout in Southern Appalachian small streams seldom feed in water temperatures above 65 degrees or below 45 degrees. Thus, fly fishermen here actually have a very narrow window during the Spring and Fall when the fly fishing is at its peak and the rest of the time, special tactics and techniques must be employed.





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Bill Bernhardt

Professional Guide and Instructor

Harper Creek Fly Fishing Company