The second I felt the jolt, I raced to take up slack line. I’d always dreamed of hooking a big coho salmon on the fly, and now—wading knee-deep in the Egegik River, which feeds Alaska’s Bristol Bay—my rod was bowed deeply.

Around my feet, swarms of crimson sockeyes moved upriver, but my fish was farther out, in dark water. I tried to gain line, but the salmon hardly budged. I was stunned that I’d already hooked a fat coho, much less without the help of bait.

To my surprise, though, the fish made no big charges for open water. After a five-minute struggle, I eased the salmon into the shallows, where I could get a decent look, and saw that the big coho I knew I’d hooked had transformed into a midsize humpy, the ugly sister of the salmonid family. The fish bobbed in the current, my fly snagged through one of its fins.

David Stumph, one of our guides, couldn’t keep from laughing. Another fisherman joked that he wouldn’t serve a humpy to his mother-in-law. I turned the fish loose with a pang of defeat and watched it disappear into the Egegik.

This was my first trip to Alaska, and five fellow anglers and I had hit the salmon run at its peak, in mid August. The cohos, or silvers, were pushing up the Egegik by the thousands to reach their spawning grounds in the tributaries of Becharof Lake, the ­second-​­largest freshwater body in Alaska. A storm had crept over the tundra the night we arrived, bringing with it rain and sharp winds, but we’d set out that first morning undeterred and eager. We’d fished baits and spoons early in the day, and I’d landed four nice keepers. But I’d lugged a fly rod some 3,000 miles from home and was determined to put it to use. After a lunch of fresh salmon chowder, we’d fanned out in the shallows along the bank, where, late in the day, I’d hooked the humpy.

RELATED: Alaska Salmon Fishing on 25 Dollars a Day

We began our second morning at the mouth of a feeder creek. I quickly caught three cohos on bait and spoons. Fooling them wasn’t difficult on conventional tackle, I learned, but it was fun. Still, after landing those first few cohos that morning, I committed to using my fly rod until I landed a real slab.

Although coho salmon are threatened or endangered throughout much of their historic range in the contiguous U.S., their numbers have held strong in the Egegik, as well as in Bristol Bay, the world’s largest salmon fishery. The Egegik district is also home to the world’s second-largest run of sockeye salmon; and chum, kings, and pinks are also bountiful. All told, the river and its tributaries contribute north of 10 million adult salmon to the Bristol Bay fishery each year, securing its place among the world’s premier salmon rivers.

On our third morning, Stumph suggested that I tie on a purple leech pattern, an old favorite of his. I soon fell into a trance of stripping and casting, stripping and casting, as I scanned the tundra. This part of the Alaska Peninsula isn’t what you find on postcards. Sand flats and shallow ponds pock the landscape, dispersed among an endless, rolling plain of sedge and shrub. But this desolate vastness is why the region remains one of the wildest places on earth, and explains why it’s been so fiercely defended against development, such as the proposed Pebble Mine.

After an hour or so, the leech fly suddenly stopped on its downriver swing, and my line shot tight. The fish ripped through the water, darting right to left. I’d never hooked anything so bent on breaking off.

After a solid fight, I brought the salmon to hand—a respectable 8-pound coho, lean and strong. I was proud. But now I wanted a fish to really remember.

We slipped into a rhythm during our week on the Egegik. We’d wake up and look for fresh grizzly tracks in the mud around camp. After breakfast, we’d catch a couple dozen fish among us, and then cook a few keepers on the shore for lunch. In the afternoons, if we got tired, we napped on the soft tundra moss. If we got thirsty, we drank river water from our hands. One afternoon, we nymphed for Arctic char; on another, we explored an abandoned trapper’s cabin. At night, we poured buckets of hot water, heated by woodstove, over our heads to rinse off.

By the final morning, I could have returned home more than content, having landed another seven or eight decent cohos on the fly. I had failed to hook a true trophy but had mostly resigned hope of doing so.

Another fisherman and I wandered down to a small point upriver a quarter mile. I was casting and stripping but not giving it my full attention. After a dozen or so casts, my line stopped and I thought I’d snagged another humpy; the fish had the same sort of dead weight to it. Annoyed, I began to strip in line hard. But the fish wouldn’t give. Then, slowly, it began to cruise along the bottom. Each time I eased the fish to shore, it would dart toward deeper water, unzipping the line I’d just reeled in. This was no humpy.

I’d fought the fish for 30 minutes when it made its biggest push, charging toward the middle of the river. After a bit more give-and-take, the coho finally surrendered. Stumph netted the fish and handed it over to me—16 pounds of pure, muscled silver. The purple leech fly dangled from the corner of its big crooked kype, right where it should be.

A good egg cure starts with an intact skein, or membrane, says Scott Haugen, author of Egg Cures, who leads a fishing school on the Egegik. First, lay the fish on its back to settle the skein, he says. Then insert the knife into the vent and ­begin slitting up the belly. As you cut, slip two fingers into the cavity along opposite sides of the blade to lift up and push apart the skin. This will guide the knife and help avoid nicking the eggs.—J.R.S.

To book a coho trip, contact Becharof Lodge.

This story appeared in the June–July 2017 issue with the headline “Searching for Silver.”