.......................  ......Fly Fishing Yellowstone National Park

11/22/11
Fishing Cold Water - Part Three
Trout don't position themselves or hold in cold water in the same places that
they occupy in warm water. Several factors account for this. One is that oxygen
is not a problem. Cold water holds more dissolved oxygen than warm water.
From an oxygen standpoint, the trout could position themselves anywhere in the
stream if the water is cold. In warm water they must position themselves in water
that is aerated enough to provide the oxygen they need. This is usually the
faster moving water of runs and riffles.

Trout in warm water have a high rate of metabolism. They must eat a lot of food
to survive. They will position themselves where ever they can acquire the most
food. This is usually the current seams and almost always is in faster or
moderately moving water. In cold water, the trout have a lower rate of
metabolism. They need less food to survive and they don't have to position
themselves in the faster moving water to acquire enough food to survive. If they
did, they would expend more energy and need even more food. In cold water
they position themselves in the slower moving water.

That seems to make it simple until you try to determine where slow moving water
exist in a stream. In the freestone pocket water streams of Yellowstone Country
slow water exist not only in the places you can observe from above the surface
but also in the area of fast moving water below the surface. Every rock or
boulder in the stream changes the flow of current and the speed of the water.
There is water moving very slow, some almost still and some that moves only
moderately even in the fast runs of the streams. In fact these obstructions can
cause the water to flow in the opposite direction. If we see this situation on the
surface, we refer to it as an eddy.

Determining where the slower moving water exist in the streams is not exactly
easy to do. The trout don't necessarily hold in shallow water around the edges
of the stream, behind large boulders and other places where the only slow water
in a stream appears to be. They can find slow moving and even still water within
areas of the stream that from the surface appears to be only fast moving water.
In many cases they can position themselves near or on the bottom and be in
water that is barely moving downstream. The deepest spots in a stream usually
have slower moving water due to obstructions upstream that are located at a
higher level or elevation. That is why they are the deepest spots. That is why
you will often see trout in clear, cold water appear to be lying on the bottom of
pools and areas of water where you can clearly see the bottom. They can also
be near or on the bottom in areas of the stream that is moving very fast on or
near the surface. In those cases, you cannot spot them. In fact there are usually
more trout holding in those areas than they are in the deeper areas of slower
moving water such as pools.

Unlike many anglers think, trout don't position themselves in cold water on or
near the bottom because the water is warmer. First of all, it isn't any warmer and
secondly, they could care less anyway. They are perfectly comfortable in cold
water that is forty degrees F. They position themselves there to be in slow
moving water that is safe from overhead predators. They can find slow moving
and even still water on and near the surface in most streams and they will
occasionally be found in such places; but, anytime they are positioned in
shallow water they are subject to being eaten by predatory birds and mammals.
They will normally only move to shallow, slow moving cold water when there is an
ample amount of food there. For example, when the Blue-winged olives begin to
hatch and the water temperature is only in the high forties, they will move in and
out of the shallow, slow moving water to feed on the blue quill nymphs and
emerging duns because that is where they hatch.  

Now you may think from what I have said so far that there is a very simple
solution. Just fish the deepest water in the stream. That is not a bad idea but
doing so isn't exactly easy. Fishing a fly that moves at the same speed other
drifting food is moving near the bottom in deeper water is not an easy thing to
do. In fact it is quite difficult to do in most cases. For example, trout holding in
deep, slow moving water of runs have the advantage of being concealed by the
broken surface of the fast water above. They are hidden from you and that puts
you into a blind fishing situation. You don't know exactly where the slow moving
water is. Even worse, you will find it very difficult to get the fly to drift at the
speed of the slow moving current in the deeper holes and pockets of the run.
That is because the current near the surface above the slow moving current on
the bottom is moving very fast. Even when you weight the fly and get it down,
the fast water on the surface pulling on your leader and line sweeps you fly
through the slow water on the bottom much faster than natural food drifts in the
slow current. The fast moving fly may even tend to spook the trout holding in
such places. Imagine what happens when the trout are holding in slow moving
water near the bottom and suddenly a fly shoots through their home at the
speed of light.

You can resort to fishing the slow water on the bottoms of the pools. The
problem with fishing for the trout holding in the slow moving water where you can
see them is that they can also see you. Trout holding near the surface have a
very small window of vision. Trout holding in deep, clear water have a very large
window of vision and can detect objects above the surface much easier and
much farther from them. Another inherent problem is that when your fly is
moving slowly through their home they can get a very good look at it. They fly
needs to look more realistic than one moving at a fast rate of speed.

Both types of water creates yet another problem for anglers. You simply cannot
present your fly to a lot of trout in any given amount of time. It is slow fishing.
Making short, upstream cast to surface feeding trout gives you a lot of shots in a
short time at the fish feeding there. That isn't the case when you are presenting
your fly to trout positioned in deep water - especially when they are not going to
move but maybe a few inches to eat anything.

So far, all I have done is tell you about some of the problems you face in fishing
cold water. I haven't told you anything you can do about the problems. I think
you can see why catching trout in very cold water isn't easy. To Be
Continued......

Copyright 2011 James Marsh