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Fishing Stoneflies
Issue 7 Number 3

Fall, 2009


The Original Online Magazine Dedicated Exclusively to the International Angler

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The Colorado River was relatively low for the middle of May. A weak mass of cold air had pressed it's way into the Colorado high country the day before, glazing the snow shrouded mountains and abruptly stopping the late spring thaw. Within a day or so, the river had cleared enough to reveal the layout of the stream bottom. New runs and depressions created by the grinding, plowing action of moving ice could be seen from each old vantage point Jim used to scout the river for trout.

Jim said he tried to ignore annoying memories of unfulfilled promises of grand, hook-jawed trout from past visits to the Colorado river. Instead, he said, he chose to believe he had learned from failure and was now better prepared to crack the code of the regal giants he knew the river held. Jim's confidence renewed after a long winter of waiting, the depths of the big, deep holes were far less intimidating. With each searching look at familiar stretches of water Jim suppressed every notion that the watery fortress could frustrate him again. This time, Jim said, it would do more than only give up smallish fish not yet wise enough to have remembered last year's lessons about hooks.

Struggling to push their pale blue heads out from under the matted, brittle remains of last autumn's grasses and cottonwood leaves, delicate pasque flowers solemnly herald summers advance. Bebb willows along the river's bank have begun pushing leaves out of the soft green buds that dot their ruddy colored, thinly tapered stems. Hearing our footsteps, a rabbit, startled from it's feast of tender willow shoots, rushes away. 

Stoneflies were migrating - hatching if you will - intent on duplicating the mating ritual their parents completed several seasons ago. Along the bank, a procession of dark chocolate colored stoneflies marched toward shore leaving tiny tracks across muddied rocks exposed by the sudden drop in water level. They advanced toward the willows and the sheltered undersides of everything within short flying distance of the river, breaking out of their shucks, unfolding their wings and scurrying over each other continuously until the romance was over.

In a quiet pocket of water on the downstream side of a large rock, a strong, noisy swirl called Jim and I to attention. A moment later, another splash of water dashed against the rock. There was no question any longer - a trout of major proportions was methodically terrorizing a procession of stoneflies. So relentless was that great trout's feeding that it stirred Jim to think it may be easy to catch with the right fly.

Hungry for a bend in his fly rod, he decided to chance taking the fish. Jim began by studying the water to judge it's flow. Satisfied Jim understood the river's direction, Jim wiggled ten feet of line out from the tip of his rod and worked his fly down around the backside of the rock. As soon as the fly came into the trout's view it took - hard. Jim struck back immediately, knowing he only had a split second to set the hook or forfeit any chance of landing the beast at all. A frantic leap revealed it's bulk, a sleek 19" brown trout still somewhat lean from winter. Jim strained to keep the fish in shallow water, knowing that if the brown reached the main current and ran downstream, Jim would have to go after it over a hopeless jumble of accumulated debris. The tippet held as Jim maintained pressure.

A few minutes later the brown lay at Jim's feet. With a simple push on the hook and a muscular thrust of the brown's tail and the trout was gone, no worse for the experience. Later that day Jim managed to fool a dozen other trout, equal in their appetite for stoneflies as was the first. The spell had been broken.

At no other time do large trout feed as voraciously on aquatic bugs as during the stonefly hatch. Having principally become predators of smaller fish rather than strict insect eaters, out-sized trout simply cannot ignore the presence of the largest aquatic insect in the stream.

Stoneflies emerge shortly after trout have come out of a long, hard winter. Water temperatures rise slowly to summer levels; currents are often swift that make demands on the strength reserves of fish; dirt and debris is being washed downstream, limiting the ability of trout to spot food in discolored water. Given such formidable conditions, it is no wonder big trout relish any and all stoneflies that happen by. In fact, many older, savvy trout will actively look for stoneflies.

To find the insects, trout will hold in places fish would normally not find nymphs. Many larger trout will brave exposure to predatory fish-eating birds and mammals just to take advantage of stoneflies. Effectively hidden by relatively opaque water of spring run-off, trout become quite bold, occasionally holding in water just deep enough to hide them. Other factors also come into play. Trout don't like having to filter dirty water through their gills; slower water near shore is cleaner, unable to hold silt particles in suspension. The fact that trout willingly seek out the large bug makes fishing for them all the more exciting. It is wonderful to discover the places big trout will hold to get their fill of stoneflies. Of the many stonefly species, larger ones attract the attention of big fish.

The two largest and most important stoneflies found on western waters are the Giant Black Stonefly, (Pteronarcys californica) and the Golden Stonefly, (Acroneuria pacifica). Wherever these two stoneflies are found in good numbers, big trout are also found. Stoneflies require unpolluted, fast flowing waters with bottoms paved with large rocks. Unlike other aquatic insects which hatch on a yearly cycle, stoneflies remain nymphs for an average of three years before journeying to shore to hatch. As a consequence, stoneflies of varying size are always present for trout. For example, after a particularly severe period of precipitation, water levels rise quickly, dislodging many of the hiding nymphs, washing them downstream where trout quickly take advantage of their sudden presence.

Stoneflies molt during their growing cycle to make room for their expanding bodies. Once, during a trip to the Colorado River, Jim and I experienced a mass molting by thousands of stoneflies during a brief period late one morning. Within minutes, a flotilla of empty stonefly shucks drifted by in the river, evoking a sudden and brutal attack on the shucks as they were being washed downstream. Jim quickly changed to a stonefly pattern of equal size and color to the drifting shucks. Jim took several good fish within half an hour. However, it didn't take long for the fish to realize that these vacant shells of the real thing had no substance worth exerting themselves over. Just as abruptly, the trout quit feeding. Until the molt had begun, Jim had spent a long morning practicing casting. Now, there was only one thing left to do...get in the car and rush downstream to where the fish would surely assault the empty shucks again as they passed. It was a good plan.

During their exodus from the river prior to hatching, stoneflies migrate laterally towards shore across the river bottom, exposing themselves to trout looking for an easy meal. Emergence generally begins at night and lasts into the morning hours. Once out of the river, stoneflies seek shelter in the branches of willows, rocks or trees. There the stoneflies allow their skins to air-dry, to become brittle and to split open introducing the winged adults to life above water. After hatching, adult stoneflies begin mating immediately. Soon after mating, the female stonefly sails over the river, depositing her fertilized eggs. Skipping across the water, dipping her abdomen into the surface, she allows her eggs to fall to the bottom, thus completing another cycle of a stonefly life. Female stones will typically make several journeys over the river surface.

Clumsy fliers under the best conditions, stoneflies frequently miscalculate their sweeps to the surface, crash into the surface and become hopelessly mired in water. Their wings become too wet to allow them to fly free and their bodies become too heavy to lift. When that happens, trout will exhibit slashing strikes for the hapless adults. When water is clear enough to allow trout to see to the surface, casting a dry stonefly pattern provide what many consider the epitome of freshwater trout fishing experiences.

When conditions on the West's great rivers are ideal, anglers frequently will travel from all parts of the country just to fish this hatch. Even when water conditions aren't perfect, you can find casting dry fly patterns under overhanging willow branches quite rewarding. Big trout will often take up temporary residence in shallow water to slurp up any love struck stonefly that falls off a branch, blown off by a sudden gust of wind.

Imparting action to the fly is an important ingredient to imitating struggling insects properly. Presentations need not always be delicate. When stoneflies hit the water they do so noisily. Fish know that and often close in quickly, possibly anticipating what fell in.

As other hatches do, stonefly hatches progress upstream, starting first in the lower reaches of the river, playing itself out far upstream. As with all aquatic insects, stonefly hatches are triggered when water temperatures reach optimum degree. What that temperature happens to be depends on the river. Day by day, stoneflies will hatch progressively farther upstream until the hatch is over for the year. Sudden changes in weather can alter the predictability of the hatch however, slowing it at times, or, stopping it altogether until conditions improve.

Be diligent and watchful when planning your trip. Allow yourself the flexibility to intercept the hatch when it offers the best chance of catching it at it's peak. If you can arrange it, make contact with a reputable guide and plan to fish the hatch according to the annual time table for the hatch. As well, arrive with a good supply of stonefly imitations in your fly box. Even when there is no major stonefly activity on the river you're fishing, stoneflies are always excellent patterns to use during times when no other obvious feeding activity is going on.

Even during low flows of the late season, drifting a stone through deep runs will often produce trout when all other fly patterns fail to interest fish. A highly productive technique often used by knowing fishermen uses a weighted stonefly nymph as point fly on a two fly set-up, with another smaller nymph on a dropper. A dropper fly can be any nymph pattern resembling other species of aquatic insects found in the river. The reasoning behind the special rigging is both sound and simple - it makes sense to use weight that catches fish!

stones.jpg (10589 bytes)



Golden Stone size 6-12 Black
Mono Stone size 4-8
Montana Stone size 4-10
Bird's Stone size 6-12
Black Swimming Stone size 6
Rubber Leg Stone size 4-10
Tarcher Stone size 4-10

Dry flies:

Fluttering Stone size 4-8
Sofa Pillow size 4-8
Dave's Adult Goldenstone size 4-8


The most productive method for fishing a stonefly nymph is the dead-drift presentation. Have both weighted and unweighted patterns in your fly box to help you fish all depths. Also, many guides recommend having patterns tied to imitate a stonefly nymph's appearance when it is tumbling with the current. When a stonefly is being washed downstream at the mercy of the current, it curls up into what might be called a fetal position, roughly the shape of a "C". While trout will take both the standard version or the curved type, having both styles along to allow you to switch  if the fish become selective is a good idea.

The most widely used rigging has the nymph tied on the point of your tippet section. Add some form of weight above the fly - usually 12 - 24 inches above the point fly. Casting this fly - weight arrangement is hardly pleasant or practical so many nymph fishing masters rely heavily on the "lob" cast. The lob cast is a short line variation of the roll cast where you cast upstream, allowing the nymph to sink to the bottom, then  raise the rod tip as line and leader approach you, dropping the rod tip as it passes. Once the fly is well past you and the fly has buoyed up near the surface, the rod tip is simply lifted and cast in one stroke, pointing the tip where you wish to place the fly and going through the motions of fishing out the cast all over again.

When short-line nymphing this way, it is paramount the fly be on the bottom. If you do not feel your fly bouncing along the bottom every other cast or so, add a little more weight. Many fly shops carry moldable lead putty that works extremely well for this style of nymph fishing. You can add or subtract the putty with ease as you wade from one piece of water to the next. Split shot has a tendency to damage leaders which weakens it whereas soft lead doesn't. Also, soft lead is less likely to snag, is reusable, and stays on the leader quite well after it hits cold water and hardens somewhat.

Leaders can be relatively short - from six to 10 feet long tapered to 2X or 3X, heavier if water conditions are particularly murky and lighter if clear. Lastly, always keep your hooks sharp - bouncing stoneflies along rock covered bottom dulls them quickly. Armed with knowledge of the right techniques, flies, and a stonefly rich river, any angler can find productive satisfaction in "romancing the stones".



  • Colorado River, Colorado - Mid-June between Grand Junction to Lake Granby. Best stretches are from Kremmling to Hot Sulfur Springs.  Black stoneflies in sizes 4 to 10.
  • Gunnison River, Colorado - Mid June, depends on water discharges from dams. Black Stonefly.
  • Dolores River, Colorado - Variable, spring, depends on water releases from Mc Phee Reservoir. Golden Stone, size 6-12.
  • Blue River, Colorado - Hatch erratic due to water level fluctuations. Golden Stone, size 6-12
  • Frying Pan/Roaring Fork Rivers, Colorado - Early June to mid June. Black stonefly.
  • Henry's Fork, Montana - May and early June. Black stonefly.
  • Rock Creek, Montana - early June. Black Stonefly.
  • Clark Fork, Montana - early June. Black Stonefly.
  • Madison River, Montana - mid June to early July. Black Stonefly.
  • Blackfoot, Montana - mid June to early July. Black Stonefly.
  • Yellowstone River, Montana - early to mid July. Black stonefly.

Copyright, 1989 by Tony Oswald


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