I'm not a fisheries biologist, a geologist nor a hydrologist. However, I hold
a B.S. degree in Forest Management and took several elective courses in Fisheries,
Hydrology and Geology while in college. The extra coursework covered fish biology,
stream geology and hydrology.
What you are about to read is the result of my constant learning process over
the years, regarding trout streams and why they act like they do. I recently finished
compiling this bit of work and it has been invaluable to me in my quest to become
a better trout fisherman. Being able to read a stream is just as valuable to a trout
fisherman as the ability to read a defense is to a quarterback. I enjoy the study
of trout streams and I'm happy to share some my findings with you.
There are many types of trout streams and their geology affects stream hydrology
and hydrology affects the species of trout that can survive and do well. Dams also
play an important part in stream hydrology and what the stream offers in the way
of trout and what species of trout are best suited to it. Keep in mind that trout
are cold water fish and you won't find them where the stream temperature gets much
above 75 degrees.
Take the meadow streams of the west with their lush green grass, beautiful wildflowers,
rainbows and browns, cutthroats and easy wading. Then there are small mountain streams,
with their "pocket water" where you rarely wade, but walk from pool to pool hiding
behind vegetation along the banks and stealthily flip your fly under an overhang
on a pool or run, trying to outwit the cutthroat and the tiny Brook Trout. Perhaps
the most beautiful of all trout is the Golden Trout found only in the "ice-cold"
mountain streams and lakes of the High Sierras, as we near 10,000 feet in elevation.
We all know of the fabulous "Spring Creeks", fed by groundwater emanating from
springs flowing out of limestone outcroppings. Spring creeks usually have their "headwaters"
in or near the head of a valley floor which leads to a more gentle gradient, (slope),
but still have enough movement to oxygenate the water. Spring Creeks are clear and
the water quality is superb, which produces lush aquatic vegetation. Rainbow, brook
trout, and brown trout abound.
Freestone streams usually arise from a source other than a spring and are fed
by seasonal rains that fill lakes behind dams, whereby the tail waters are cold enough
to support cold water fish. Then there's runoff from snow melt, or glacial melt,
such as the mountain streams in the Rockies with their browns, rainbows and cutthroat
trout. These streams come rushing down the mountains in a series of pools, runs
and riffles as they make their way to the valleys below, where they normally feed
water storage reservoirs that ultimately release water used to irrigate crops or
for industry and by fly fishers and most importantly, drinking water. There are other
streams located in climatic areas where the climate itself prevents air temperatures
and ultimately the water temperature from becoming unbearable for the fish. Again,
we find rainbows, brook trout and browns.
The world renowned Chalk streams are restricted by geology to southern and eastern
England and are fed by water from Cretaceous chalk aquifers. Their temperature is
mostly constant throughout the year. Chalk streams are rarely subject to floods or
droughts. Runoff is minimal and Chalk Streams are more stable than other types as
a result. Chalk streams, like Spring Creeks somewhat limit pool-riffle development
because of their gentle gradient. Water quality and clarity is generally good. This
promotes a healthy environment for the Brown Trout, insects and aquatic plants.
Dams can have a tremendous effect on trout populations. Not all streams and
rivers have dams, but those that do have what is called "Tail Water" or a "Tail Race".
Tail water is that which flows out of the gates of the dam that holds back the stream
or river. Dams are built for flood control and hydroelectric power generation and
storage reservoirs to hold water for later use. Fishing hydroelectric tail waters
is an adventure and can be very dangerous if you're caught on the tail water when
water release starts. Hydroelectric dams are required by law to have a warning device
that alerts anglers that water release is imminent. Fishing can turn from great
to poor in a matter of minutes because of the rapid rise or fall of the water emanating
from the dam.
Rainbow and brown trout inhabit these waters.
In addition to hydroelectric dams, there are diversion, top draw, (top and bottom
draw), whereby the layers of water behind the dam are mixed by alternately releasing
from the top and bottom and lastly, bottom draw dams, (dams that release water at
the bottom of the dam, whereby the coldest water from the bottom layers of the lake
flows out), In the south, bottom draw dams enable trout to exist where it was once
impossible. Water flowing from a bottom draw dam will be around forty-five to fifty
degrees in temperature. This makes it possible for a river to have a thriving trout
population in the southern states. Examples of rivers with bottom draw dams and
trout tail waters are the White River in Arkansas, Guadalupe in Texas, San Juan in
New Mexico, Lee's Ferry in Arizona, Chattahoochee near Atlanta, and the South Platte
Again, rainbows and browns are common.
Canyon Lake Dam, on the Guadalupe River near New Braunfels, Texas, the southernmost
trout fishery in the United States is a bottom draw and as long as the water flow
doesn't fall below 200 cubic feet per second, the water will remain below 70 degrees,
even in the long, hot Texas summers. The result is a self sustaining twelve mile
long trout fishery. I know it's hard to believe you can catch trout in South Central
Texas, but you can also catch trout in any tailrace water in the south that has stocked
trout and receives cold water from a bottom draw dam flowing at a rate that will
keep the water temperature at or below 70 degrees.
Some of these rivers, (tail waters), will over a period of years develop a reproducing
trout population. The Guadalupe River Chapter of Trout Unlimited, (GRTU), of which
I am a member annually in December and January, stocks the Guadalupe with around
30,000 rainbow trout averaging a pound to a pound and a half. Later, when we see
trout fingerlings in the river, we know they are not hatchery fish, but are from
eggs from a female rainbow trout that has made it through the previous year. The
record Guadalupe rainbow is 8 1/2 pounds. While rainbows on the Guadalupe have thrived,
we recently stopped stocking browns because they have never reproduced and do not
Fisheries biologists across the country are experimenting with rainbows raised
in lake or stream pens. These pens hold tiny rainbow trout during the fall and
winter months in hopes of teaching them how to feed and better survive the cold winter
months. They are fed several times daily and by living in pens actually placed in
a lake or stream, they are protected from larger fish and other predators. In this
manner, the fry will thrive and grow and gain knowledge of lake or stream foods that
they can eat.
Pen-raised trout are released into a stream when they reach about a pound in
weight. They are more akin to wild trout in their stamina and are better able to
survive simply because their mouths are large enough that they can feed on stream
or lake minnows. Planter fish from hatcheries have mouths too small to swallow minnows.
Penn-raised trout also have a better flavor than hatchery fish. Pen raising definitely
works, but the problem is having enough large pens to produce enough surviving rainbow
fry that grow to release size to make the project worthwhile. GRTU tried this several
years ago with a few small pens in the Guadalupe River with limited success.
If you'd like to know more about fishing Tail Waters, get Ed Engle's book "Fly
Fishing the Tail Waters" – Stackpole Books – 1991. Ed is also a columnist for several
US fly fishing magazines.