Big Lost River Idaho
North Fork Big Lost River sign
Copyright 2018 James Marsh
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Fly Fishing the Big Lost River Idaho
The Big Lost River has two main branches that flow
together to form its main stem. They are the North Fork
of the Lost River and the East Fork of the Lost River.
Both these creeks flow through some of Idaho's most
beautiful, wild and rugged country among mountains
with peaks as high as 12,000 feet. Fly fishing the Big
Lost River provides some very diversified opportunities.

The North Branch is a small stream that starts in the
Northwest area of the drainage. It is stocked in some
areas and provides good, easy fishing, especially
around the bridges and campgrounds.

The East Fork of the Big Lost River drains the southern
area. Its trout are wild but the access is limited. There
are some special regulations in force to help keep it a
designated "Wild Trout" fishery.  The fish are mostly wild
rainbows and cutthroat trout.

The main stem of the river below the confluence of the
North and East Branches is not as good of a fishery as
the East Branch. There are not as many trout but
access is plentiful and easy. This section also has some
special regulations. The main stem flows through some
beautiful, scarcely populated country.     

The large variety of different types of trout make the
fishing very interesting. Rainbows, browns, brook and
cutthroat are the main species but there are some Bull
trout and some Golden trout. All of them are wild.
Type of Stream
Freestone Stream

Rainbow Trout
Brown Trout
Cutthroat Trout
Brook Trout
Bull Trout
Golden Trout
(Wild and Stocked depending on the

Central Idaho

Small to Medium - 75 miles long

Nearest Towns

Varies depending on the location


Special Regulations
Yes, on the East Branch and Main

Non-Resident License
State of Idaho

National Weather Service Link

Fly Fishing Gear and Trout Flies

Stream Flow Data:
Real Time USGS Data (Arco)
Big Lost River Idaho
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The Idaho fishing season runs year-round.
Fly fishing the Big Lost River is good most of
the year.

It is possible to catch trout but it is usually
very tough fishing during the winter.
The best time is the springtime except for
the time runoff occurs.
Big Lost River Fly Fishing Guide
The strategies and techniques used for fly fishing the
Big lost River depends on the branch you are fishing
and the water levels. 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.
Big Lost River Hatches and TroutOur
information on aquatic insects is based on
our stream samples of larvae and nymphs,
not guess work. We base fly suggestions on
imitating the most plentiful and most
available insects and other foods at the
particular time you are fishing. Unlike the
generic fly shop trout flies, we have specific
imitations of all the insects in the Beaverkill
River and in all stages of life that are
applicable to fishing. If you want to fish
better, more realistic trout flies, have a much
higher degree of success, give us a call.  We
not only will help you with selections, you will
learn why, after trying Perfect Flies, 92% of
the thousands of our customers will use
nothing else.

The hatches on this trout stream can be
especially good. The water chemistry is
suitable for a large variety of aquatic insects
including the famous Salmonfly.

During the winter, the hatches consist mostly
of Blue-winged Olives. These hatches can
occur from late November until near June.
Several species of
baetis exist in the river.

Midges are the only other substantial
hatches that occur during the winter months
and imitations of their larva, pupa and adult
stages of life can produce well at times. You
can actually catch trout on midge imitations
whenever you choose to fish. It's just that
they may be the only thing hatching on most
winter days.

Little Yellow Stonflies show up during late
May and can hatch until late June. The
Yellow Sallies can be an important insect to
imitate during this time. Hatches are normally
very consistent. The Salmonfly nymphs
usually start moving to the banks to hatch
during the middle of June. Hatches are
normally over by the middle of July. Golden
Stoneflies follow just behind the Salmonflies
and also start appearing in June. They can
last until near the end of July.
Hatches, continued:Other than the
BWOs, the bulk of the mayflies will be the
Pale Morning Duns. They start hatching
in June and last into the first of August.
The Blue-winged Olives (baetis) mayflies
will reappear during the month of August.
Hatches of these little mayflies can last on
into September.

Caddisflies are the most consistent
hatches of aquatic insects. Little
Short-horned Sedges and Green Sedges
(Rock Worms) hatch starting in May and
last through June. Different species of
Spotted Sedges start in early June and
hatch until late September. They
represent the most important caddisfly
hatches. There are several more species
of caddisflies but they are not usually
heavy hatches.

Terrestrial insects become important
during the month of June. Imitations of
ants, beetles and grasshoppers can
produce until as late as the end of
September. The huge amount of tall
grass that line the banks provide the
perfect habitat for the hoppers as well as
the other land based insects.

When the water is high, streamers can
sometimes produce. Heavy weighted
streamers like the Zonker can be used to
hang some of the large rainbows at times.

Specific imitations of the Little Yellow,
Golden and Salmonfly stonefly nymphs
are important flies to have. Imitations of
the BWO and PMD nymphs are also
effective for sight fishing during low, clear
water conditions. Of course we
recommend our "Perfect Flies" not just
because they are the most realistic
imitations but also because they are also
the most productive flies you can
purchase. Imitations of the stonefly
nymphs have been proven to work on the
Big Lost River.
Summertime fishing depends on the
amount of rainfall and the depth of the
snowpack but it is usually very good.  
Early fall can be a good time if the water
levels are okay.
James Marsh fishing Big Lost River
James Marsh Big Lost River
Options For Selecting Flies:
1. Email us (
with the dates you will be fishing this
stream and we will send you a list of our
fly suggestions. Please allow up to 24
hours for a response.

2. Call us 800-594-4726 and we will help
you decide which flies you need.

3. Email us (
with a budget for flies and we will select
them to match the budget and get them to
you in time for your fly fishing trip.

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