Blue-winged Olives are very
common in the park and usually
exist in large quantities. There are  
many different species of them.
Golden Stoneflies are very
common in most of the park's
streams. They can really turn the
trout on for some fast action.
Aquatic Insect Hatches:
............................              .Fly Fishing Yellowstone National Park
Caddisflies of many species live in
the park. To be successful on
many of the streams, you must
know how to fish the caddisfly
Small Western Green Drake
You will find that the Yellowstone National Park
has a huge diversity of aquatic insects. This
large variety of insects has caused many
anglers to shy away from trying to determine
what insects the trout may be feeding on at any
given time and place.

Other Aquatic Insects:

Many anglers are of the opinion that hatches are
not important in the park. This same line of
thinking is largely responsible for those same
anglers labeling fishing conditions as excellent,
good, average and bad. When they fail to catch
trout using their standby methods and fly
patterns, they sometimes falsely assume that
fishing is bad.
In general, determining what food the trout are
taking is just as important in the park as it is in
any stream anywhere in the nation.
Hatch Intensity:
Most anglers haven't seen large hatches such
as they can see at times in the park, especially
on the Madison, Firehole and Yellowstone
Rivers.  They are, for the most part, not aware
that hatches on the other small, headwater
mountain streams can also be prolific.  In fact,
hatches in Yellowstone National Park are often
as prolific and as common as they are
anywhere, if you compare them to other
headwater, mountain freestone streams.
Pocket Water:
One reason for the lack of consideration for
hatches in the park is the fact that attractor
patterns work very fairly well in some of the
streams. This is not a product of the park itself
rather the type of water found in the park. Much
of the water is pocket water. Without going into
detail let us just say that in many situations the
trout simply do not have time to closely examine
the fly.
Slow Moving Water:
When they do, they can be just as picky as trout
found anywhere. Many anglers fail to catch trout  
when they are in the smoother flowing, clear
water or slow to moderate smooth flowing
shallow, low water conditions. They usually just
ignore the pools altogether and for good
reasons. The attractor flies perform very poorly
where they can closely be observed by the trout.
Some of the streams such as the Firehole and
Madison have slow to moderate currents that
are very tricky. The water swirls from the grass
and the currents run at different speeds.
Conflicting currents are the normal thing. This
makes for tough conditions of presentation and
for the fly pattern. Many of the streams, such as
the Gibbon and Belchler Rivers have meadow
sections that have slow to moderate water that
is slick and tough to fish. In these locations the
fly can be very important because the trout get a
very good opportunity to examine the fly closely.

Examples of Selective Feeding:
These are some of the aquatic insects that can
cause selective feeding in Yellowstone's
streams. There are others but these are some
of the most common.
PMDs or Pale Morning Duns:
The pale morning duns are one of the mayflies
that can cause trout to feed selectively. This can
be a frustrating hatch. Trout can even become
selective on one stage of the hatch and pay little
attention to the other stages. This happens
often with the emerging stage of the mayfly.
Trout will take the easy way and eat them when
they are emerging just below the surface.
Blue-winged Olives:
Blue-winged olive hatches that usually occur
during the first part of the season and again
during the latter part of the season can cause
trout to become selective on them in some
streams. This can be challenging fishing,
especially on the smooth flowing streams.
The huge salmonfly nymphs can certainly
cause the trout to feed selectively in some
streams but probably not as much as the
average angler expects they do.
Golden Stoneflies:
The Golden Stoneflies can really confuse the
match the hatch situation. Often when both the
adult salmonflies are still around the golden
stoneflies are hatching. The trout can ignore the
egg laying salmonflies and eat the emerging
golden stoneflies.
Western Green Drakes:
Certainly at the right time on the right stream the
trout can become selective on the Western
Green Drake. This is a large mayfly and where
they hatch in large quantities, the trout will
usually concentrate on them.
Thumbnails-Click on images.
Rainbow Trout
Flyfishingdvd's Imitating Aquatic
Insects: Stoneflies  
will teach
you what you need to know about
stoneflies and how to imitate
their behavior.  
Please CLICK HERE to sign up       
for our catalog, press releases      
and information on Yellowstone     
Fly Fishing
Fly Fishing DVD's
Mayflies -Guide to
Imitating Aquatic
Insects teaches you
how to fish all the
mayfly hatches.
Mayfly DVD
Click below for a
list of flies for
Oxygenated Water:
Normally some trout, especially the rainbows,
can usually be found to some extent in the fast
moving, pocket water. One reason for this is
that during the hot summer months of the year
on some lower elevation streams the water
temperatures in the park are on the warm side
of that preferred by trout. Since warm water
holds less dissolved oxygen the trout have to
seek the oxygenated water to survive. During
this time they tend to stay in the faster water
such as plunges, runs and pockets.
Standby flies such as the Adams, a pattern that
to some extent imitates any mayfly and maybe
even some caddisflies, often work well.
Some of the very high headwater streams in
the park have a low PH.  In this type of water,
the insects have little to feed on. Insects that
feed on algae exist in these types of streams
but not in large quantities. Acidic water doesn't
contain much plankton or algae. Several
species of aquatic insects exist in large
enough quantities to cause the trout to feed
selectively in the park.
Opportunistic Feeding:
In most of the small pocket water type
streams, most often the trout are feeding
opportunistically. In other words they eat a
variety of food and sometimes just about
anything they can find.

Selective Feeding:
Trout can and do feed selectively in the park.
There are usually several different species of
insect available for the trout.  When trout select
only one species of insect, or other food for
that matter, and feed on it exclusively, there's
always an abundant amount of the food
available. They do this because they can feed
more efficiently. They feed heavily on the most
prevalent food and ignore the others.  They no
longer have to resort to looking for food. They
can stay in one place and eat all they want.
They can maximize their food intake while
minimizing their energy expenditure. This is
not a choice the fish makes. It is a trained

Impressionistic Imitations:
Generic imitations, sometimes called
impressionistic imitations, work often when
specific imitations do not. If an angler is using
a specific imitation of something the trout are
not feeding on, then they may be better off with
a generic imitation that represents a variety of

Specific Imitations:
On the other hand, often when the trout are
feeding exclusively on insects of a certain
species in the park, anglers fail to catch trout
consistently because they do not use a
specific imitation.  This occurs far more often
when the trout are feeding on nymphs, larvae
or pupae stages than it does when they are
feeding on insects on the surface of the water.
Underwater selectivity is the least understood
topic in fly fishing for trout. The reason is very
simple. You can't see what the trout are eating
under water very well and usually, not at all.
During these times most anglers are satisfied
to believe that fishing is poor. They fall back on
the stereotyped labels for fishing conditions.

Different Viewpoints:
Marine or fish biologist (behavioral scientist)
tend to believe that fish feed only
opportunistically. If trout were not somewhat
selective, they would starve. They can tell the
difference most of the time in tiny leaves, twigs
and other stuff that look somewhat, at least
from an impressionistic standpoint, like little
insects. They eat a few things by mistake but
not much or they would starve. They can dang
well rise beneath your fly on their way to eat it
and suddenly turn away from it, rejecting it.
When that happens they are being selective
about what they eat. Selectivity is not
something that is either in effect or not in effect.
It is a matter of the degree it exist at the
particular time and at the particular place. Don't
misunderstand me please. It is just a matter of
definition - selectivity and the angler sees it or
selectivity as the scientist see it.
continued Examples of Selective

Flavs or Small Western Green
The Small Western Green Drake
is also plentiful in some streams
in the park, especially the Firehole
River. The trout can become
selective on them.
Gray Drakes:
The Gray Drake is common to
many streams in the park. Where
the are, Slough Creek for
example, they can cause selective
Spotted Caddis:
Certainly the very common and
very plentiful spotted caddisfly can
cause the trout to feed selectively.
This can go on for quite a while in
the summer on some streams.
Little Sister Caddis:
Not as plentiful but existing still in
large quantities is the Little Sister
Caddisfly. We have seen the trout
become selective on these. The
lower section of the Gibbon River
has a large hatch in July.
To be successful fishing the various streams of Yellowstone National Park, an
angler must understand the different types of water and the hatches. Attractor
patterns will work in some cases and not in others. You must know when and
where these difference occur.
You must also understand the behavior of the aquatic insects in order to catch fish
consistently. Just having he right fly is not enough. You must know where and
when to present it and how to present it to be successful.

Copyright 2011 James Marsh
Mayflies: Fly Fishers Guide to
Imitating Aquatic Insects,  lets
you see the naturals, learn to
identify mayflies, and  match
the hatch. It includes Eastern,
Mid-western and Western
Mayflies, including the
nymphs, emergers, duns and
spinners. Learn the
successful strategies for
imitating mayfles.
2 DVD Disc:  $29.95
New For 2011
Yellowstone National Park
"Perfect Fly" Selections

Best  Yellowstone National
Park Fly Selection:
Includes 108 flies that imitate the
vast majority of the most important
foods trout eat in Yellowstone
streams. Save $25.10 over the
regular price.

Click Here For Detailed Information

Good Yellowstone National
Park Fly Selection:
Includes 82 flies that imitate the
most of the important trout foods
trout eat in Yellowstone streams.
Save $14.60 over the regular price.

Click Here For Detailed Information
We will help you select flies
for your Yellowstone trip.
Just call us Toll Free at
800-594-4726 or email us
and tell us when you will be
fishing. Although we can
arrange faster delivery,
please allow  five days for
normal delivery. Shipping
in the U.S. is free. We will
select the flies based on
the insects that will be
hatching at that time.