Fly Fishing For Trout In Hot Weather
by James Marsh
August, 2019 Issue
Copyright 2019 James Marsh
Silver Creek Idaho
During the past many years of trout fishing, we have often been concerned with the warm water temperature issue
while fly fishing for trout during the hot summer. Water temperature is very important anytime of the year, but
especially during the hot Summer season.
The subject of water temperature and oxygen content of the water comes up often during the hot summer. The
water temperature issue even becomes important in many of the western Rocky Mountain trout streams.
There, the early morning air temperature often starts out at about thirty-five degrees but reaches as high as
ninety-five in the afternoons. I could probably write a book about the subject of fishing for trout in warmer than
normal water, but for those just getting started, I will get straight to the point. We don't catch or release trout
when there's a reasonable doubt as to whether or not the fish will live after being released. We don't have to
worry about whether they will live or die because we make sure we don't fish when they are subject to dying
from warm water. In marginal water temperatures, we make sure we don't over stress the fish and that we fight,
hook and release them as rapidly as possible.
When you frequently catch and release every trout a lot of trout year-round, you would have to be plain stupid
not to realize when the trout could become stressed. You should never guess at the water temperature. We
usually carry two thermometers and check the water temperature almost every day we fish, especially if there is a
question about it being too warm or for that matter, too cold.
The amount of dissolved oxygen in the water is directly related to the water temperature. In case you don't
already know, cold water holds dissolved oxygen much better than warm water. The effects of water
temperature on the amount of dissolved oxygen doesn't change at a constant rate. It changes at an
In general, for most species of trout, the fish are most active when the water ranges from about 50 to 65
degrees. The cold-blooded trout feed at the maximum rates due to their metabolism level in this temperature
range. From 65 to 70, the accelerated rate I referred to begins to take place to the point it becomes a big
factor. In simple terms, at 65 there's no problem and the trout feed aggressively. At seventy degrees, there
can be a problem depending on the type of water. The dissolved oxygen content can be too low.
Still water is one thing and fast, turbulent water is another. The amount of dissolved oxygen will vary greatly.
That's why you hear advise to "fish the oxygenated water" all the time. When the trout start suffering from the
lack of oxygen, they will begin to cease their feeding activity. It's not a great deal different from the way they
react in very cold water. It is just due to a different reason.
When the water temperature reaches about seventy-four degrees, the trout just about have to have highly
oxygenated water to survive. Again, keep in mind that these temperatures are guidelines. Again, the particular
species of trout and its location and more specifically the type of water it is in will vary this somewhat - not
greatly, but a little.
All of us that want the fish to survive, want a safety margin. We don't want to catch a fish that shows signs of
being stressed. When you climb a high mountain, especially in the eight to ten thousand foot elevation range,
you will probably be short of breath. You may have to sit down to rest occasionally. Just as you will probably
struggle for breath at times, under the same conditions, the trout will stop fighting as hard. If the trout is in your
hands being released, it won't be difficult to hold. When you put it back in the water (which should be done just
as quickly as possible), it may hesitate before leaving. A trout that isn't stressed won't swim off slowly. It will
shoot off like a rocket, as Angie often says. If the water is too warm and the trout rolls over, or is slow swimming
away after being released, it's probably stressed from the lack of oxygen.
Does this mean the trout will die? Probably, not any faster than you would when you give out of breath
climbing a mountain. It probably puts the fish at some risk, but just how much risk depends on a many factors.
Back when I fished professional bass tournaments, which had penalties for dead fish, there have been times I
wanted to give bass mouth to mouth recitation, only to see them active as they could be in the live well a few
Many believe that bass or trout will swim off and die after being stressed during the fight and then released.
According to many studies that have been done on this, the results showed that they usually don't swim off and
die. The great majority of them will probably be just fine. Of course, every once in a while, one may die, but my
guess is that in ninety-nine percent of the cases, it would be a result of the fish being mishandled. They can be
out of the water too long. They can be handled with dry hands and even placed on dry ground or rocks and
die from problems due to that. They have slime on their bodies for a good reason. Removing it by mishandling
the fish, is a much bigger problem that fighting a fish a little too long in marginal water temperatures.
When you are fishing streams that begin at high elevations, if there's any question about the water temperatures,
fish at higher elevation - an elevation where the water isn't too warm. Take the water temperature. Don't guess at
it. If it's below (lets say, sixty-eight degrees), catch all you want and just make sure you release them as quickly as
possible. If it's warmer than that, or has the chance of getting any warmer, I would suggest you look for another
Perfect Fly Stream Thermometer:
Knowing the temperature of the water can be critical in determining the timing of aquatic
insect hatches and the activity level of trout and other species of fish. This is an excellent
thermometer that we have used for years for taking the temperature of the water in
streams and lakes. It works fast and is easy to read.
Click Here for more details: