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Not far from the bustling tourist center of Ketchum/Sun Valley, Idaho, there is a lightly fished tailwater with reliable hatches and great dry fly fishing to healthy rainbows. The stream is Big Lost River near the small farming town of Mackay (pronounced "Mack-ee").

The Big Lost fishery is overshadowed by the well-justified reputations of Silver Creek and Big Wood River. However, the Big Lost tailwater flowing from Mackay Reservoir holds a good population of two- to four-pound trout, with some fish reaching 23 inches and eight pounds. This is an underappreciated quality fishery.

The Big Lost River heads in the Pioneer, Boulder, and Big Lost River ranges at elevations of 11,000 to 12,000 feet. Its various forks are captured in Mackay Reservoir, located a few miles north of town. Flows from the dam are regulated for agriculture with many diversion ditches supporting the potato and grain fields south of town.

This fishery is located due east of Ketchum/Sun Valley with unpaved road access over scenic Trail Creek Pass. Alternatively, highway access from Ketchum is via Highway 20 through Craters of the Moon National Monument to Arco, then north on Highway 93, a drive of about an hour and a half.

What makes this tailwater fishery special is its solitude and great sightfishing opportunities. The first several miles of stream below the dam flow through a healthy cottonwood forest. The river structure retains a freestone character with riffle, pool, run, and some braiding around small islands. The river is not wide: it is as narrow as 20 feet across in some places. Generally the water is crystal clear, offering good sight-fishing opportunities with nymphs during times of no surface activity.

Another appealing aspect of this fishery is the scenery. Mount Borah, Idaho’s tallest peak, is located just to the east in the Big Lost range. But I equally enjoy the rundown character of downtown Mackay. Here, there is a mix of small businesses, some operating, others abandoned. It could have been the movie set for The Last Picture Show. From the frenetic pace of downtown Ketchum teeming with tourists, here only a short drive away, Mackay is a slow-paced retreat. It’s like traveling in a time machine back to 1950 middle America, the days before fast food restaurant and motel chains. Here, the dinner choices are mostly steaks and salad bar. No chichi California cuisine is served in Mackay.

For years I co-owned a cottage near Silver Creek. The cottage was for me a twice-a-year getaway. I originally concentrated on the demanding spring creek fishing of nearby Silver Creek or the freestone charms of Big and Little Wood rivers. It was only through an introduction to Big Lost from my neighbor, Dave Glasscock, that I came to know of the Big Lost fishery. Dave is coauthor of the definitive guidebook to Silver Creek (Silver Creek: Idaho’s Fly Fishing Paradise). He is a longtime outfitter, fly fishing guide, and owner of Idaho Angling Services (

In 1990 I had just returned from a three-month sabbatical in New Zealand. Dave, who has spent many winters there, encouraged me to explore Big Lost, saying that the sight fishing there would remind me of my South Island trout-stalking experiences. He was right, and I was sold on Big Lost. Over the years I came to treasure time in Mackay and on Big Lost – so much so that during a 10-day fishing vacation, I would spend half my time in Mackay.

But be forewarned that there is one big negative to this tailwater fishery: limited public access. However, over the years I have come to see the limited access as a positive rather than a negative. In Idaho, it is lawful to walk or wade up- or downstream so long as you are below the high-water mark. So an angler’s main challenges are to find a lawful access point and then spend the effort needed to gain some solitude. This assumes that the releases from the dam are low enough to allow easy wading or travel along the gravel banks of the river. I personally found that mid-September into October were ideal from flow and hatch perspectives.

During the fall, the wading/walking conditions are ideal and the transition between Trico and BWO hatches offer hours of daily dry fly action: small flies and big trout. In many spots, large rainbows will feed heavily in only inches of water. And the shortened daylight hours of fall fishing concentrate the action into bankers’ hours, another seasonal bonus.

As for access points, the most obvious are the sportsman’s accesses off Highway 93, one located near the dam and the other two miles farther downstream. Recently, however, an additional public access point has been created in town, where a generous landowner donated land and Idaho Fish and Game built a small parking area and trail. There are other little-known access points, but these require local knowledge.

I don’t mean to suggest that the great fishing available in this backwater is limited to the fall. Prior to the irrigation season (which usually starts Memorial Day weekend), springtime BWO hatches can provide steady action. Once the irrigation season starts, the water is higher and it is worth hiring a knowledgeable guide with local knowledge of alternate access points and where to go, as the little yellow stone and PMD hatches in late June and early July provide some of the best fishing for the entire season.

Large crane flies usually appear in late July and early August. The locals use a big, unbelievably ugly fly dubbed a "Mackay special" to imitate the crane flies. I have fished the river in the summer months and had consistent success with terrestrials or nymphs to sighted fish. Summer is a time when popular waters around Ketchum are heavily fished. Big Lost is a great alternative summertime destination.

Oh, a final word about the name of this river: Big Lost River is a sink river. About 25 miles south of Mackay, the river’s waters disappear into the volcanic strata of the Arco Desert. Hydrologists claim that the Big Lost waters reappear as part of the Thousand Springs of the Snake River, an underground trip of more than 80 miles.

Altogether, Big Lost River offers terrific fishing and a time-travel opportunity back to an earlier, simpler time.
Bill Owen.

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