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

02/02/12

Fishing Cold Water - Part Eleven
It isn't easy describing various sections of streams that vary greatly in size. Just
for one example, if I use the word "pool", a large stream in the lower elevations
can have a very large pool that's several feet deep, whereas a large pool in a
middle elevation stream may only be three feet deep. I really should use a
program that allowed me to illustrate cross sections of the streams to help
explain what I want to point out. I just don't have the time to do that. In past
articles on fishing cold water, I pointed out two things to consider - the depth
and speed of the water..

Depth:
When the water is very cold, lets say less than 45 degrees, trout don't
necessarily get in the deepest water that's available. That doesn't offer the fish
any advantage. The water temperature isn't any warmer at the bottom and they
don't need the extra depth for protection from their predators. I'm pointing this
out to make sure you don't think I'm implying that trout will seek the deepest
water in the stream. The depth they choose is more a product of the amount of
light penetration. This is controlled by sky conditions and water clarity. For
example, If the water is stained and again, still or moving slowly, trout may hold
in very shallow water. If the water is very clear, still or moving slowly, and it's up
in the day and the skies are clear, the trout will tend to hold in deeper water.

The only thing that will change this situation is a concentration of food and
again, that's the exception, not the rule. A developing hatch is the only thing
that's going to create a larger concentrate of insects. When the water
temperature is less than 45 degrees, there's very few insects in the streams  
other than Midges that hatch. Some species of Blue-winged Olives hatch in the
high forties, but not the low forties. Some streams have some little Winter
Stoneflies but that's about all the aquatic insects that are going to hatch in water
that's very cold.

Speed:
Finding still or slow moving water in a pocket water stream isn't as easy as it
appears to be. That's because slow moving water can be found beneath fast
moving water on and near the surface. When the surface of the water is rough,
meaning not smooth and slick, your view of  what's below the surface is
distorted. The trout's view of what's above the water through their relatively
small window of vision is also distorted by the rippled surface. That helps to
keep them hidden from predators. Trout will hold below fast water with a rough
or rippled surface. They will also hold under plunges with lots of bubbles on the
surface. Just because the surface of the water is rough and moving fast doesn't
mean that all the water below the surface is moving fast. There can be very slow
moving water below fast surface water. It can even be moving in the opposite
direction of the surface water - an underwater eddy. It's even possible that
there's slow moving water two or three feet below a plunge at the head of a
pool.  

If the surface of the water isn't broken, meaning it's flowing slow and smoothly,
using polarized glasses you can see the bottom of deep water on a clear day,
provided the water is clear. If you carefully examine the water from a low
vantage point below the trout's line of vision, you can see trout that may be
holding in the deeper water. They are not easy to see, but once you get used to
what to look for, you can spot them if they are there. It's areas of water that's
below the fast water with a broken or rippled surface that's hidden from your
view.

If the bottom of a stream is relatively flat, the speed of the water on the bottom is
usually close to the speed of the water near the surface. If you fished the deep
water on the bottom of such an area when the water is very cold, you would be
fishing an area that wasn't holding any trout. If someone simply "presented their
fly on the bottom of the deeper water of a stream, they may be fishing water that
doesn't hold trout much of the time they are fishing. It depends on the stream's
bottom configuration, but you may well have to fish a long time before you get
lucky enough to be presenting your fly in an area of water that's moving slow
enough to hold cold water trout. To offer someone such advise as to "get your
fly on the bottom of the stream" is really worth very little. It doesn't eliminate
much water.

Any upstream obstruction on the bottom of any particular area of a stream
causes a change in the speed of the water on or near the bottom. For example,
the water down in smaller size holes in the bottom surrounded by water that's
shallower than the hole is usually still or moving slowly. More often, slow water
on the bottom of a stream is caused by the same thing that causes it to move
slowly on the surface of a stream - upstream obstructions. Picture a typical large
boulder that protrudes above the surface of a fast water stream. The water has
to flow around it, usually around both side of it. The water behind it ranges from
almost still to moving slowly, and sometimes, even in the opposite direction. In
other words, it is obvious there's a small "pool" behind every large boulder in
the stream that protrudes out of the water. What isn't so obvious is the fact
there's also a slower moving area of water downstream of every large boulder
that's below the surface of the water.

In the above scenario, I used a large boulder to help illustrate a place that the
speed of the water changes; however, it doesn't take a large boulder to do that.
Every rock that protrudes above the bottom of a stream creates the same
situation. It doesn't take a very large rock to create a "volume" of slow moving
water that's large enough for a trout to hold in when the water is very cold.
Again, if there's enough light and the water is clear, you can spot these
underwater obstructions but only if they are under water that's relatively smooth.
You can't see these types of obstructions under fast water with a broken or
rippled surface.

In some cases, large boulders that protrude out of water create a deep enough
pocket of slow moving water to hold trout in cold water. Holes behind large
boulders are worth fishing if they are deep enough to give the trout protection
from overhead predators.

Copyright 2012 James Marsh