The South Fork of the Boise: A River in Change

Located less than an hour and a half from The Idaho Angler in
Boise, Idaho is a river known to locals as simply the “South Fork”.
Although the South Fork originates miles above Anderson Ranch
Reservoir, the tailwater below Anderson Ranch Dam is where the premier
fly fishing takes place. The South Fork of the Boise River has been and
still is a world class rainbow trout fishery. Anderson Ranch Dam was
completed in 1950 which turned this freestone trout stream into a trophy
trout tailwater. It received its blue ribbon trout stream designation over
thirty years ago.

Whether it’s your “go to” wadeable winter fishery or your favorite
float trip during higher summer flows, this river has become a staple for
fish crazed individuals from Boise to Sun Valley and beyond. Late summer
through the end of trout season, March 31st, the river is generally at an
easily wadeable level. From opening weekend (Memorial Day weekend)
to late summer, with higher irrigation flows, you can float or wade the
river. The wading at this time can be challenging due to these high flows.
The flows for the river are controlled by the Bureau of Reclamations.
The upper ten miles are friendly to drift boats and rafts alike. From
Danskin Bridge to Neal Bridge, there is a roadless stretch known as the
“canyon” with stouter class 3 and 4 rapids. This is where the more
adventuresome boaters use rafts and pontoon boats, which are more
suited for this section.

This past summer on August 8, 2013 The Elk Complex Fire was
created by a convergence of several fires started by lightning strikes. This
massive, hot burning fire scorched 131,000 acres in three weeks and
torched most of our beloved south fork. The fire was declared 100%
contained on August 31, 2013. This alone was devastating to many anglers
who considered this river their home waters. Even after the fire was out,
access was denied to the public due to safety issues. The worst, as some
people expected, was still to come. Although much of the riparian zone was
not burned, the hillsides were charred. Some worried that the lack of
soil stabilizing vegetation on the canyon walls would turn the loose soil
into giant slides that would reek havoc on this recreational gem.
Unfortunately, on September 12, 2013, a rain storm dumped about a half inch
of rain in a very short period of time. This event triggered five major mudslides
that will change the land and waterscape of the south fork for
years to come.

With the help of The Idaho Angler, I am writing a blog for as long as
there is interest, on the impact of the fire and post fire events and the
subsequent recovery of the South Fork of the Boise River. Over the next
several years I will be answering questions, conducting interviews,
providing photos, and sharing personal experiences as well as the
experiences of others. I started my quest for answers to the impact of the
fires and mudslides by taking a trip down to the river on November 10th to survey
the damage first hand. I plan to observe and report on the river regularly
into the future.

Let me start by saying that I was happy to see that the entire river
corridor had not burned to the ground. There are large areas which
have not been torched. I was ,however, taken aback by the magnitude of
some of the fire damage and the enormous effects of the mudslides on
the landscape and the river. Taking pictures to represent the aftermath of
these events just didn't do these events justice. To comprehend what
happened this summer you have to see the barren hillside and stand on
the mud flows for yourself. You will see the large areas that burned, and
the millions of cubic feet of dirt, rock and woody debris that the hillsides
have shed.

After experiencing the new look of the South Fork for myself, I took
a trip down to Idaho Fish and Game. Armed with questions I sat down
with David Parrish, Sport Fishing Program Coordinator. I also spoke with
Joe Kozfkay, who is the Regional Fish Manager. They are both upbeat
about the future of the South Fork and want the public to know that
although the fires and mudslides were catastrophic events they did not
effect the river in a catastrophic way. And in fact, during my recent trip to
the South Fork I saw decent hatches of midges, blue wing olives, and a
larger mayfly that I believe was a mahogany. I also saw numerous fish,
large and small, feeding on them.

The mudslides filled the river with massive amounts of debris. Some
of this is good and some of this is bad. The bad is that there is an
enormous amount of silt and rock that has filled in many of our favorite
holes and runs. It has also clogged up areas used by insects and
spawning fish. I was assured by Idaho Fish and Game that over the next
several years the higher water levels, that we normally see in the spring
and early summer, will purge the river of the damaging silt. The river
would benefit greatly from a good flush this year. The water behind
Anderson Ranch Dam is currently at 24% of its regular capacity. So
unfortunately, even with a spectacular snow pack this winter, the chances
are slim that we will see flows over 2,000 cfs (cubic feet per second) this

Here’s the good; along with silt came woody debris, carbon
(charred wood), and spawning size gravel. Woody debris is an important
part of the ecosystem for fish and insects. It is an integral part of habitat
for juvenile trout during the winter months and for larger trout during the
higher flows of spring. The water coming out of the dam is actually a fairly
sterile environment. The woody debris will benefit the river because it
will help recharge the system with organic materials. The carbon that has
entered the water system through ash and burnt pieces of wood will also
help boost the water quality below the dam. Years ago while I was
guiding in Montana, I was told that the insect hatches were tremendous
in the years following the great fires in Yellowstone Park.
The river has been lacking in adequate spawning size gravel for
years. The gravel that trout prefer is 1/2” to 3/4” in size. Now there are
great new spawning areas downstream of each mudslide.
Another high note is that the young of the year, that would have
emerged from the gravel last July, seem to have survived the events.
Idaho Fish and Game did find several hundred dead fish floating where
the South Fork and Arrowrock Reservoir converge, but fortunately, the
dead fish were primarily suckers and whitefish. There were nominal
numbers of small Kokanee and trout, but the numbers were not what you
would have expected. I was surprised to hear the fish kill was as minor as
it was. David Parrish told me that half the water column must be
suspended materials to effect the trout to the point of suffocation.
Estimating population loss would be purely speculation at this time.
The Idaho Fish and Game has decided to move their 3 year fish survey up to
the fall of 2014. This survey will give us a much better idea of what the
effect of the fire and the slides truly were on the trout population.

It is also interesting to note that there are three distinct “lakes” on
the river that were caused by the mudslides. These lakes are anywhere
from .2 miles long to .6 miles long. The first new lake is located around
the Tailwater boat ramp. The second lake, which was existing (1996) but
made larger, is located above “the slide” area. The last new lake is
located a mile and a half downstream form the Cow Creek bridge. I
would expect the debris dams to be washed out with higher spring flows
but only time and water will tell. It will be interesting to see what
happens to these debris dams and to see if boats will be able to navigate
through the new material in the river. Hard sided boats may take a
beating this summer in this new riverscape.

We are not out of the woods yet. The South Fork below Anderson
Ranch Reservoir will be prone to more mudslides. Rain and snow melt
will put more silt into the river until the vegetation stabilizes the hillsides
again. It is going to be a few years before the river and the canyon are
stabilized and take on a more permanent look.The biggest loser in this
giant domino effect of nature will be the deer that use the drainage as
a wintering area. There may not be enough forage for the deer to make it
through a tough winter. Keeping the deer wild is Idaho Fish and Game’s
priority. As a last resort, feeding the deer would probably be done using
alfalfa pellets.

I feel much better after doing my research on the fate of the South
Fork of the Boise River. I hope this blog answers some questions,
motivates people to check out the river for themselves, and accept what
has happened. I also hope this encourages people to share their
experiences good and bad. I’d like to hear from you, Email me at

I want to give special thanks to the following; The Idaho Fish and
Game for taking time to answer my questions. Roger Phillips, from the
Idaho Statesman, for keeping us up to date on the events as they were
unfolding, and to the Ted Trueblood Chapter of Trout Unlimited for
organizing the planting of over 280 trees in the effected areas.