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Fly Fisherman, 1978 – A Stillwater Secret

An important early-season insect in ponds all over the country, the water boatman is too often overlooked by fly fishermen

A Stillwater Secret by Gary LaFontaine

During the spring thaw the drive over the dirt to check the pond became a ritual, a performance necessary every five days or so to ease the tensions of a fishless winter. By late April, the snow had melted, puddles were collecting on the ice, and small wedges of open water were forming in the shallows. Finally a warm wind arrived in the hollow, breaking up the cracked shell ice and mixing the waters of the pond.

I parked the car and trudged over the soggy meadow, bypassing the lower basin. After circling the rusting hulks of gold-dredging machinery, I climbed a waste pile of gravel and sat there to watch the welcome spectacle of some 20-inch fish cruising the shallow cove below.

I sneaked down and started roll-casting with a new type of fly pattern, following a plan I had thought through a thousand times during the past winter. I brought the fly back with a fast retrieve and one of the trout rapped it solidly, but I flinched so hard on the strike that I snapped the 6x tippet.

Some stones rattled down from the hill where a man and women were walking along the crest. They stopped and stared at me, clinging to their spinning rods and cans of bait. I quickly cast again, hoping they wouldn’t come down and wanting at least one fish in case they did decide to fish and spooked everything back to deeper water.

After I hooked and landed two fo the big browns, I called up to them, “There’s room on the other side of the cove”.

They sat on rocks until I caught a third trout. “I’ve been fishing this spot for three days,” the man said loudly to the woman. He stood up and more stones clattered down the slope, popping along the edge of the water. “The son-of-a-bitch comes here and makes it look easy.”

“Easy?” I yelled as they started to walk away, wanting to run up there and tell him about the four fishless years here, the long days of frustration when these same trout snubbed every fly, the experimental patterns and techniques that had failed.

“I never caught anything,” he shouted at me as he left.

At various times during the year a common beetle-like insect—the water boatman (Corixidae)—becomes a prevalent aquatic organism in numerous ponds and lakes around the country. The insect goes through a developmental cycle that includes and egg, five nymphal stages, and the adult. The adult overwinters—usually hibernating in the bottom mud, but sometimes swimming around under the ice—and mates in early spring. Throughout the fall, winter and early spring, as different populations of boatmen peak, the insect assumes great importance in the diet of trout, because the populations of other food organisms are apt to be at the low point (in terms of availability to trout) in their respective seasonal cycles.

Every fish from the Gold Creek Dredge Ponds that I checked contained fresh water boatmen in its stomach, but I had never worked up an exact imitation of the insect. Scud, damselfly nymphs and midge pupae triggered obvious spurts of selective feeding in the stillwater environment, but when the trout fed on the boatmen, their activity always seemed random. At least that was the case until Galen Wilkins and I encountered a “fall” of egg-laying boatmen.

On an early-spring afternoon, we passed the back cove of the pond—this bowl of clear and shallow water was usually fishless—but we stopped in awe on the hill when we spied trout cruising just under the surface. The entire basin was jammed with large browns.

Egg-laying insects hit the smooth surface, spun in frantic circles to pierce the surface tension and dove for the bottom weeds to lay their eggs. The fish were frantically intercepting the bugs falling all over the cove.

This feeding spree turned us into total bumblers, but we finally managed to lengthen leaders and tie on flies. After we went to opposite ends of the cove, where we could easily crisscross the whole pothole, we failed to cast with any forethought. We scattered tosses to any fish that swirled and changed flies every few minutes; our sloppy flailing neither put down nor caught any of the trout.

I admitted my own loss for an immediate idea. “I’ve never seen a feeding pattern like this.”

“What’s causing it?” Galen asked.

“Water boatmen,” I answered, but that knowledge didn’t help. The color, size or shape of the fly weren’t the primary factors in selectivity. The fish were keying on the splat, fuss and dive of the insect, and none of the flies we carried had the physical properties necessary to mimic that telling action.

Our search for a solution to this problem started with references in American angling literature—Fishing Flies and Fly Tying by Bill Blades and Matching the Hatch by Ernest Schwiebert—but although the books had valuable information on the life history of the order, the recommended fly patterns were not satisfactory for matching the diving motion of the insect.

While gathering facts on the water boatman, we found that the phenomenal feeding triggered by this egg-laying process wasn’t limited to a single pond. Not only did the sprees occur on other still waters in western Montana, but far-ranging fishing friends reported the same activity scattered throughout the west.

During a trip for Kamloops rainbow in British Columbia, I encountered a fall of water boatmen in the bay of a small lake. The trout fed in the same manner, cruising not so much in schools but as individuals, a fish actively chasing an insect as it crashed on the surface. All my casting produced only a single trout, but the six-pound rainbow was crammed with boatman adults.

We dumped adults into an aquarium at the Angler’s Agency in Deer Lodge, Montana where they carried through their egg-laying process. We watched them shug along the surface and then dash in a slanting dive to stick their eggs to the weeds. We listed the visible characteristics of the insect that might control selective feeding by trout. There were, in order of importance: the shimmer of enveloping air globures, size, shape and color. In watching them further, we became more certain all the time that the most important recognition factor for the trout was the peculiar activity of the water boatman.

Bill Seeples provided a clue as he sold flies to a customer. He recommended one of my patterns, a Natural Drift Stonefly Nymph,  saying, “It’s not enough for a fly to look like an insect, it has to act like one.” He dropped the artificial into the aquarium where the pattern sank with its head upright. “That’s the way the real stonefly holds itself when it drifts in the current, and this fly is carefully balanced with lead wrapping to act just that way,” he explained.

I looked at the tank and thought: “If we can tie a fly to balance head up, we should be able to tie one to balance head down.”

Graham Marsh and I sat down at the fly-tying bench, putting together prototypes and dropping them into the water. Finally, we constructed an imitation that tipped head first and sank—a pattern that would “dive’ with proper rod manipulation.

The pattern is fished with a sinking-tip line, which sinks faster that the fly so that at the start of the retrieve the imitation dives downward. The rod tip should be poked into the water at the completion of the cast and, after a short pause, the retrieve carried out with quick steps.

The Diving Water Boatman solved another feeding puzzle as well. The swirls and dashes of marauding trout in the pond shallows during the fall were also made by selective fish concentrating on individual boatmen swimming to and from the surface to replenish their air supply through the surface tension. The action of our pattern mimicked the antics of the naturals returning from the surface.

Whe Fred Arbona and I seine-tested the Dredge Ponds in late September, each scoop of the net revealed why trout preyed almost exclusively on the water boatmen. Every sampling produced hundreds of active boatmen but only minor population of mayfly nymphs and olive scud. The food supply was so limited in variety during the autumn that a fly fisherman needed only four or five patterns to match any feeding situation.

During two years of testing, the Diving Water Boatman proved indispensable when trout were feeding on naturals. In difficult waters—those high-fertility ponds that are cold enough to support trout—this specific imitation has often been the solution for selective fish in the fall and spring.

The basic pattern has been successful for angling friends in Idaho, Wyoming, California, Colorado, Oregon, Washington, New Mexico and British Columbia. It should also be important in the eastern United Stated and eastern Canada, where trout ponds at higher elevations often hold good populations of water boatmen. All over the more northern sections of the country, when many early-season streams are apt to be high and cold, anglers should be looking to trout ponds, who in turn will be looking at the ubiquitous water boatmen.