THE YELLOW HAZE
It starts here in the western United States in mid-June in most years and its appearance is greatly anticipated by fly anglers. They come from the far corners of the globe to Montana, Wyoming and Idaho to experience it and only rarely does it disappoint. The yellow haze is caused by the appearance of what has been described as the most important fly hatches in the western states; the insects that comprise the flies commonly referred to as PMD's – Ephemerella infrequens and Ephemerella inermis. [New names – if you care – Ephemerella dorothea infrequens and Ephemerella excrucians] There are also other insects that are a similar yellowish color that hatch during this time of the year, in the east, Midwest and west, but the insects that are called PMD's by anglers are what cause the greatest amount of attention.
Early season mayflies are most dark in color and as the season progresses the insects that make up the summer hatches tend to be lighter in color. Then, as autumn approaches the mayfly hatches become darker in color. It is the consensus of many entomologists that this color shift is in response to the warmer temperatures in the summer months. In the spring dark colored insects absorb the heat from the sun more readily than light colored insects; making it possible for them to move. In the warmer months of the year the air temperature is adequate to allow the insects to move without the addition of the direct heat of the sun. In fact, the direct heat of the summer sun will quickly desiccate delicate insects like mayflies. In addition, as the summer progresses mayflies tend to become smaller; thus reducing the surface area of their bodies further reducing moisture loss due to the increasing heat. Now there are exceptions to these general rules but it is helpful to the angler to be aware of them.
Now if you take a quick look at these insects they appear to be completely yellow, but if you look at them carefully you will notice that the body color is usually infused with olive, and depending on the water from which the insect is hatching they may be quite olive. If you are a person that believes that subtle nuances of color make a difference in the success of your imitation I would suggest that you examine the insects closely before you tie on your imitation.
Fly fishers call these insects Pale Morning Duns [PMD] but I have found them hatching from morning until late afternoon. When I am planning to fish this hatch I plan to be on location ready to fish by 9 a.m. I select a place where I anticipate the hatch will appear and find a place where I can observe the water. With my Polaroid glasses and a proper sun angle I can see "beneath" the water and observe the action of the fish. When I begin to see fish beginning to move into feeding positions and starting to work back and forth I know that the nymphs are beginning to start to move around prior to hatching. A nymph pattern, my favorite being a Sawyer Pheasant Tail, fished at the proper depth will usually produce a few fish before the hatch begins.
I continue to observe as I fish, watching for the fish to move upward in the water column as the insects get closer to actual emergence. When this occurs I put on an emerger pattern and use the Sawyer nymph as a dropper. Since I rarely use a strike indicator, I grease my leader to bring the emerger closer to the surface. If you use an indicator move it closer to your emerger pattern so it will float higher in the water and closer to the surface.
It has been my experience that when you begin to see flies on the water that a productive pattern to use is a soft hackle fished right in the film. Fished with an emerger on a short dropper this can be a deadly combination. Many times I will fish this combination throughout the hatch.
The spinner fall can occur in the morning and also in the afternoon. During very hot weather I have found the spinners over the water as early as 6 a.m. I enjoy fishing the spinner fall when it occurs in the evening. Here in Montana from late June through July you can fish until nearly 10 p.m before it is too dark, and when the spinners are falling and the fish are rising there is nothing better in my book.
I have many memories of fishing this hatch, especially the spinner fall. I remember one early July evening when I arrived on the stream about 6:30 p.m. The day had been blistering hot for Montana and a late in the day thunder storm was driving across the valley hurling gusty winds, and hard driving rain. The temperature took a dramatic drop and although I loved the coolness I was afraid that any hopes of a spinner fall had been dashed by the wind and rain. Nonetheless I put on my waders, shouldered my vest and took my rod and walked down to the stream. I sat on the bank watching several Nighthawks working high above, their plaintive "peent" calls ringing out in the still evening air. Suddenly I was startled by the distinctive gulping sound of a trout rising. As I lowered my eyes from looking at the Nighthawks I could see a few spinners beginning to dance above the grass along the stream. Looking at the water I began to see an occasional rise. Tying on a rusty spinner pattern I eased off the bank and worked myself into position to drop my fly where I had noticed a trout rise. The fly settled just above where I saw the dimple left by the rising fish, it floated a few inches and disappeared in a small dimple. Moments later I slipped the net under a very respectable brown trout. Without taking it out of the net I slipped the small barbless hook out of the corner of the jaw and let the fish swim out of the net. I returned to the bank, dried my fly and watched the water. Soon I spotted another fish and I repeated the scenario, hooking and landing another nice brown. The spinner fall was never heavy but a small trickle of flies continued to produce rising fish until it was too dark to see the rises or my fly. The last fish of the night was a butter-fat Yellowstone Cutthroat that was taking an occasional spinner in a small depression that was barely deep enough to cover his back. A perfect ending to a wonderful evening of fishing during the yellow haze season.