Summer Flyfishing in the Rockies, 2021
The West is in the midst of an unprecedented heatwave, with daily ambient temperatures running 10-15 degrees above normal. In addition, the winter snowpack was less than average, and the spring rains have been nearly nonexistent. All this has resulted in the excessive warming of trout streams, and water flows 30-50% below normal.
In Montana, trout stream temperatures are closely monitored by the Fish, Wildlife & Parks Department (FWP). The FWP closes or restricts fishing when stream temperatures reach 73 degrees for 3 consecutive days. At the time of this writing, 8 streams have been either shut to all fishing or restricted to fishing from midnight to 2 PM, referred to as a “hoot-owl restriction.” Personally, I think this is awfully lenient, as trout become significantly stressed when the water temperature reaches 70 degrees. At or above this level, hooking mortality is increased when trout are caught and released. They are also more susceptible to diseases, like fungus.
So what is a trout angler to do? Fortunately, with a little research and planning, there is trout fishing available. The first step is to check the FWP website for current restrictions. The second step is to study the US Geologic (USGS) water site. Grouped by state and watershed, data is available for most streams of interest to anglers. Stream flow in cubic feet per second (CFS) and depth is generally available, and compared with historical averages. For some streams, daily temperatures are also available. I also keep a diary of streams that I fish, noting among other things, the stream flows that fish well.
Let’s first consider freestone streams, which are most affected by climatic changes. The graph below was taken from the Montana USGS site. Daily water temperatures are displayed from midnight to midnight. It reveals that during the last four days the water temperature reached its lowest point around 7-8 am, and rose to 70 degrees by early afternoon. Thus, I would plan to fish in the early morning, and finish by 11 or 12. Of course one could also consider night-fishing.
Hatches and trout behavior are both affected by climatic changes in their streams. It is beyond the scope of this blog to detail the changes in hatches. But in general, for those bugs with an annual life-cycle (most), the onset of their hatch period will begin several weeks earlier than average with sustained stream temperatures well above normal. Similarly, their daily hatch time will begin earlier, roughly 1-2 hours.
As stream temperatures approach 70 degrees, trout seek more comfortable water. Think winter in reverse. During the hot sunny afternoons, they move into deep runs and pools where the water temperatures are lower. They may also move into spring-fed tributaries or the headwaters of their streams, which at their higher elevations remain cooler.
Warm water carries less oxygen. Consequently, surprisingly large fish may be found holding in shallow, oxygen-rich riffles that they would not otherwise occupy. Look carefully, and you may see the pink stripe of a large rainbow trout or a dorsal fin protruding above the water.
Trout are “cold blooded”, and in warm water their metabolism is increased. This requires them to feed. However, rather than mid- morning or early evening, their dinner bell rings during the night and early morning, when the stream temperatures are more comfortable. Fortunately, the coincident shift in hatch schedules means that abundant fare is present.
There are of course alternative venues to freestone streams. Spring creeks, tailwaters, and deep or spring-fed lakes remain cooler despite the hot weather. So don’t let the dog days of a hot summer get you down. With a little research and planning, there is good trout fishing available.
Written by Al Simpson, July 2021.