Angie Marsh fishing Big Lost River
Big Lost River Tailwater
Copyright 2018 James Marsh
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Fly Fishing the Big Lost River Tailwater
The Big Lost River Tailwater is located below MacKay
Reservoir. The reservoir is a relatively small one with
its water levels mostly controlled by the spring runoff
and late summer agricultural irrigation needs. The
tailwater is also small, averaging only about twenty to
thirty feet wide.

Its banks are lined with high grass and cottonwood
trees as it flows towards the town of MacKay. The
fishing is greatly influenced by the water releases. At
times the water temperature can be high enough that
it concentrates the trout in certain areas of the stream.
It can also become crystal clear and require spring
creek like techniques and presentations.

During the spring when MacKay Reservoir fills up, the
releases can be strong creating high water conditions
that may not drop until the latter part of June. At that
time the flows will become suitable for wading and
fishing can be great.

The wild rainbow trout are the highlight of the tailwater.
They average between fourteen and twenty inches.
They have been taken up to twenty-five inches.
Although trout can be taken at times on dry flies,
nymph fishing is the generally accepted method of
fishing. Sight fishing to large rainbows with nymphs is
a special technique used when the water is low and
clear as gin.
Type of Stream

Rainbow Trout
Brown Trout

Central Idaho


Nearest Towns

May 24 through March 31st.


Special Regulations

Non-Resident License
State of Idaho

National Weather Service Link

Fly Fishing Gear

Stream Flow Data:
Real Time USGS Data  (Below
Big Lost River
Tailwater Idaho
100% Satisfaction Guaranteed
Although the season opens the last of May,
you may not be able to fish the river until
near the end of June due to high water
If the releases are favorable, it is possible
to catch trout during the winter.
Springtime isn't a good time to fish the
tailwater because of the season and high
water conditions.
Big Lost River Tailwater Fly Fishing Guide:
As with many other tailwaters, the fishing methods and
strategies depends greatly on the releases. This
stream has some huge rainbows. The rainbows
probably average between 15 and 18 inches. There
are some hatches but not many. When there is a
hatch, the dry fly fishing is usually great. Sight
nymphing is popular during the winter.

The dam releases greatly depends on the snow pack.
In high snow pack years, the McKay Reservoir will stay
full and the tailwater can remain high until well into the
month of June and at times, almost the first of July.
The ideal time to fish the river is when the water first
drops down to a normal or low level.  The ideal sight
fishing flow is about 175 or less. Normal flows are
about 540 early in the season and about 265 later in
the season..

This stream can become crystal clear. Catching the
large rainbows in the clear water can become very
difficult. Locals use 7X tippet and fish small nymphs
during this time but it takes staying hidden and perfect
The stream is relatively small with a lot of
trees and bushes in the water. There are
many overhanging bushes along the banks.
One you hook a large rainbow in this river,
you have usually just started the process of
catching it. Landing it is a different thing.

One of the most effective ways we have found
to fish this river is with streamers. The large
rainbows will smash a well presented
streamer. This works best very early or very
late. Many of the local anglers use a double
nymph rig. These work best in the riffles and
pocket water.

There are several very meadows with lots of
grass. Terrestrials will work during these late
summer in these stretches.
Midge fishing is also popular during the
winter. The river gets some ice but the
discharges and spring water that seeps in
the stream keeps it mostly clear of ice all

If you are planning on fishing this river,
always check the discharges and stream
flows first. Everything depends on the
water levels. They are generally high the
first part of the season but drop through
the summer and can become low during
the Fall.
Big  Lost River Tailwater Hatches and
Trout Flies:
Our 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 tailwater 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 in the tailwater 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 in the tailwater 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 tailwater.
Early summer provides the best fishing.
Late summer depends on the amount of
water being used for irrigation.
Water levels can be low during the early fall
but late Fall can provide some excellent
Big  Lost River Tailwater Fly Fishing Report:
07/06/17 The discharges are still running high, or too high to wade safely in many
places. The runoff conditions are about over and things should settle down very soon.
There are lots of insects hatching.
James Marsh fishing Big Lost River
James Marsh - Big Lost River
James Marsh - Big Lost River
Big Lost River Idaho
Thumbnails: Click on image to enlarge
Thumbnails: Click on image to enlarge
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.

All orders are shipped free in the
U. S. Orders over $100 are shipped via
Priority Mail.  
11/13/18 Fishing Report
(see bottom of page)
09/07/17 Great conditions exist right now, and we are getting some good reports. Good
discharge and stream levels making it easy and safe to wade. Hatches taking place and
terrestrials are working.
01/30/18 Just a reminder that you can catch trout during the winter. Fish as near the dam
as legal. Midges, creams and reds or blood midges, and winter stoneflies are hatching.
03/16/18 Season ends in about two week. Conditions are good now. Low discharge rates and
trout being caught on Midges and Skwala stoneflies.
05/06/18 Just a reminder that the regular season will be opening soon. Shoot us an email
and let us help you plan that next fishing trip.
06/10/18 Conditions are good and trout are being caught. Midges, March Browns, lots of
BWOs, Little Black and Spotted sedge caddis are hatching.
07/01/18 The river is turning out some nice trout. There are multiple hatches and we
continue to get some good reports. It is about as good as it gets right now.
07/20/18 The tailwater is in good shape with low discharges and stream levels easy to
wade most of the time. We are getting some good reports. Lots of PMDs, spotted sedge,
little Yellow stones and more.
08/02/18 Discharges and levels are low but sight fishing the larger browns is turning out
some good catches for a few anglers. Use light leaders and BWO nymphs.
11/13/18 Sorry for missed reports. We are still getting good catch reports from the few
anglers fishing the tailwater. Blue-winged olives, Mahogany duns, Cream midges are
hatching. Sculpin streamers are getting the larger size trout.