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Idaho Rivers: - Big Lost River
Fishing Idaho's Lost River Valley
Article by Ben Arellano of Angler Guide
Located in the heart of Idaho in probably the most sparsely populated region, the Lost River Valley runs 75 miles from Arco through the great wild-west town of Mackay and on to Willow Creek Summit south of Challis.  Dominating the valley's skyline in almost every direction are rugged mountains with several peaks reaching well above 12,000 feet in elevation.
Sagebrush and grassland canvas much of the Lost River Valley.

At 6000 feet in elevation the scenery in the valley changes dramatically. From the north end you will enter a narrow rock canyon where odd rock formations line the zigzagging highway.  As you pass through the canyon you can't help but notice exposed rock layers representative of successive steps back in time. At the end of the canyon it will give way to a elevated view of the broad Lost River Valley.  Here you will be exposed to one of Idaho's most scenic treasures. For the next thirty miles sagebrush and brown grasslands will landscape the valley. A short distance away are Idaho's two tallest mountains, the Lost River and Pioneer Mountain Ranges.  The  Lost River Range is an area of fantastic cliffs, rock folds, spires, huge peaks and vast vistas.  Of the eleven peaks over 12,000 feet in elevation in Idaho, nine are on the Lost River Range.  The Pioneer Mountains are equally as impressive with many peaks above 11,000 feet and one peak over 12,000 feet. Both are abundant with wildlife and seldom will you not see Pronghorn Antelope or Elk along the foothills of these mighty ranges.

The Big Lost River meandering through the valley floor above Mackay,  Idaho.

The Pioneers are the headwaters for the Big Lost River, a freestone river that meanders through the valley until it reaches Mackay Reservoir. Game fish species found in the Lost River Valley include rainbow trout, brook trout, bull trout, cutthroat trout, golden trout, mountain whitefish, and grayling, but the Big Lost River is a predominantly a Rainbow fishery. There are areas of excellent fishing prior to Mackay Reservoir, however much of it runs through private land. Some outfitters have elected to obtained fishing rights from these land owners, most anglers choose to utilize the public access at Mackay Reservoir.  Mackay Reservoir is a small reservoir and does have camping and boat ramp facilities and is a favorite to many retirees.   In springtime high water levels reach willows and shrubs that line the west bank of the reservoir thus creating an ideal habitat for many fish.  Fly-fisherman normally have good success catching fish in this area.  The reservoir would probably see plenty more fly-fisherman if not for the lamenting winds that hound the Lost River Valley in spring.

Below the reservoir is where the Big Lost River becomes a quality tailwater fishery.  As the river flows toward the town of Mackay the scenery changes dramatically.  Present along the river are tall cottonwoods and lush grassland.  The waters in this section can be crystal clear and much of the river is seldom wider the 20-30 feet across.  Seasoned anglers favor light tippets and many love the finesse required to fish the river.  Fishing conditions are pretty much predicated by the fluctuation in water flow.  Consequently high water temperatures are key reason why fishing drops off and this can be attributed to a variety of reasons. 

The caddis and mayfly hatches are normally in full-swing by late April on into early June. Unfortunately the river is not opened to fishing until Memorial Day weekend. Some years with a low runoff  fishing in June can be excellent and chances are good you'll end up with a finned pig if a caddis pattern is properly presented. During a normal snow-melt and runoff year, the salmonfly hatch will begin mid-June or early July.  Unlike many of Idaho's other tributaries the Big Lost does not see that much pressure during the salmonfly hatch. 

Part  2

Area Facts

Borah Peak, in the Lost River Range, is the highest mountain in Idaho. The semi-arid Lost River Range has 9 of Idaho's 11 peaks over 12,000 feet.

Borah Earth Quake of 1983 was the strongest In the Continental U.S. In 25 Years measuring 6.9 on the Richter scale.  View Articles

The Mackay Dam was started in 1906 and completed in 1930 following a tumultuous history of water wars and dynamite.

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