Copyright 2013 James Marsh
Fly Fishing Guide to the Big Lost River Idaho
This is a beautiful river most of which flows through an unpopulated area of Idaho. It flows
over seventy-five miles through the Lost River Valley, a place that looks unlike any other
Western setting. High jagged and rugged looking mountains are in full almost anywhere you
look. The Lost River Mountain Range and the Pioneer Mountain Range are some of the
most scenic of all the Rocky Mountains. The headwaters of the Big Lost form in the Pioneer
Mountains. When it comes out of a steep walled canyon in its upper end, the river flows into
a the large Big Lost Valley. The river starts near Arco and ends in MacKay Reservoir. Below
the MacKay Reservoir is the Big Lost River Tailwater. It is such a great fishery we have a
separate section devoted to the tailwater.
Even though this river is noted for its rainbow trout, it also has some brook trout, bull trout,
golden trout, mountain whitefish, cutthroat trout and even a few grayling. The streams start
out in Copper Basin, a large high elevation valley. After they merge, Trail Creek Road follows
the Big Lost River for most of its length. Most of the river in the headwater areas is lined with
sagebrush only. Downstream you will begin to see the Cottonwood trees that show you
where the river lies.
This is a true freestone stream where only rain and snow determine the amount of water that
is going to be available - that is except for the farmers. Irrigation needs can use a lot of the
streams water during dry years with little rainfall and low snowpacks. The stream has its long
sections of riffles and runs and some pools along the way. It's a pleasure to fish. Wading is
usually very easy and the fish can be fairly easy to catch even in the East Branch where they
are all wild trout.
Unlike many headwater freestone stream areas, the Big Lost has an amazing number of
aquatic insects. The populations are heavy and the dry fly fishing can be great at times. The
best water to fish is the East Branch. As I said, it is all wild trout fishing and mostly rainbows.
These trout can get up to twenty inches long. The North Branch is stocked and offers easy
fishing. The main stem of the river isn't as good as the East Branch but there are still plenty
of trout to be caught.
In addition, there is Summit Creek, Star Hope Creek, Wildhorse Creek, and what is
sometimes called the West Branch of the Big Lost. These little feeder streams offer
additional small stream fishing. The roads accessing the upper part are rough dirt roads.
Trail Creek Road over the summit is a gravel road and not really suitable for regular cars.
These areas are in remote locations but once you get there, you will most likely be the only
angler in sight. You want have any trouble finding solitude.
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Big Lost River Idaho