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

Fishing Cold Water - Part Two
The first question many anglers have is "at what temperature range should you
use a dry fly and at what temperature range should you use a nymph". First of
all, making this decision based solely on water temperature alone would be a big
mistake. There are times when you may want to fish a nymph when the water
temperature is 55 degrees F. and higher. There are also times when you may
want to fish a dry fly when the water temperature is below 55 degrees. There
isn't a definite magic water temperature range for either type of fly.

I think what many really mean by the question is "when does the water get to
cold to catch trout on the dry fly". With some exceptions I want go into, the
general answer is around 45 degrees. I have caught trout in Yellowstone
National Park on dry adult caddis pattern at slightly lower temperatures, 42 to 44
degrees. This was after the Little Black Caddisflies began hatching early in the
season following a day or two after the water temp went up to around 50
degrees. If there's a lot of food on the surface the trout will usually eat it. In this
particular case, the trout will usually eat the emerging pupae much more readily.

Generally speaking, the trout will respond on the surface very well when the
water reaches 50 degrees for a day or two. Dry fly fishing can even be excellent
at this temperature provided hatches are occurring. We generally would start
out fishing a nymph if the water temperature was below 50 degrees but again,
other things come into consideration. Trout will eat the nymph readily when the
water is between 45 and 50 degrees. They won't always hit dry flies within this
range. As a matter of fact, they rarely will do so but there are occasions where
they will. If you find the trout concentrated, when the water is between 40 and 45
degrees, you can usually catch a lot of them on the right nymph.

This brings up the question as to where to find the fish in cold water, or more
specifically on the bottom, in the mid-range depths or on the surface. There isn't
a good answer to that question. The trout may be in either of those water levels
depending on many other factors. The water temperature is not one of them.

When trout are inactive they tend to stay on or near the bottom but this doesn't
mean they are necessarily active or inactive. Just one example as to why this is
true is that the depth gives them some protection from overhead predators.
You may also find them in very shallow water and of course suspended in
between the bottom and surface in very cold water. The water temperature is
not the determining factor.

Remember, the fish are perfectly comfortable anywhere in the stream as far as
the temperature is concerned. When the water is very cold, the main thing to
look for is slow moving to still water. They want hold for long in fast water
because they will expend more energy than they can take in. The problem with
this is that you may be looking at a fast run, for example, with the surface water
moving very fast, when down near the bottom, between and behind rocks, the
water may be moving very slowly. In some cases it may be almost still, so you
cannot go by what you see on the surface. For another example, water near the
banks may be generally swift yet there's usually some pockets along the bank
where it move slowly.

In most streams with moderate to fast flowing water, trout don't seek a certain
depth from a temperature standpoint. It would be a rare situation where the
water would be warmer as the depth increased in the streams flowing. The only
exception may be rivers with very deep water. Even if the temperature changed
with depth, such as it does in still water lakes, keep in mind trout don't move to
warmer water for comfort. They will feed more in warmer water but they won't  
move strictly to seek a warmer temperature range unless there's a certain food
available within another area of water with a different temperature range.

There's one other thing I want to cover and that's "do you need to fish the sunny
areas of the water in the winter"? The answer to that (unless your fishing water
that's flowing extremely slow or still water) is no. The sun has the effect
of helping to warm the entire stream, even if it shines in only a few places. That
doesn't mean the water is any warmer in those areas where the stream is
exposed to the sun. As long as the water is moving, it makes no difference in the
overall water temperature, even in the areas the sun is shinning on the water. It
may help you keep warm but that shouldn't vary the water temperature.

As ridiculous as it actually is, the fact that anglers are sometimes cold when they
are fishing during very cold weather, allows their mind to play games with them.
Fishing the sunny spots; thinking that the trout are cold and looking for warm
water (in the same sense us warm blooded creatures get cold) may give you
more confidence but other than that, it probably won't help.  

Copyright 2011James Marsh