For the first time in years, the Bighorn River has had some high
flows. Around the 20th of June the flow reached 9,600 cfs and it
stayed there for four days and then dropped gradually to 6, 200
cfs. That is a far cry from the 1,500 cfs that was in the river May 21.
What the high flows accomplished in a few days time was to flush
the accumulated silt and detritus out of the system. Some islands
on the upper river were eaten away while new sand and silt bars
were created on the lower stretches, which will foster growth of
cottonwood and willow seedlings. Also, many of the riffles and
flats that had been silted in have been rejuvenated creating excellent
habitat for the blue-winged olive nymphs, Trico nymphs, and yellow
Sallies. Probable downsides of the flush are a diminution in scud
and mahogany nymph numbers.
Of course, the higher flows have caused the trout to relocate.
Many are holding tight to the banks while others are holding
below shelves in midstream.
The trout have gone on a feeding frenzy: with so many aquatic
invertebrates dislodged by the higher flows, there are multitudes
of invertebrates sluiced into the currents. Sowbugs, scuds,
aquatic worms, midge pupae, and mayfly nymphs seem to
be the primary critters swept away and into the mouths of
the eager trout.
The trout are plumping out. The dominant age class in the river
appears to be composed of 14 to 17-inch rainbows and browns.
These fish are sporting beer bellies due to the plentiful food supply.
The bigger trout, especially the rainbows, are recovering nicely from
the spawn with their girths growing daily. An 18-inch rainbow trout
has a girth of ten to ten and a half inches.
The trend of the rainbows outnumbering the browns in the river continues.
Fisheries biologist, Ken Frazer, guesstimated that there were at least twice
as many rainbows as browns in the upper 13 miles. (Frazer's guesstimate
was based on his observations while electro fishing the river in June and has
not been subject to population analyses that will be done this winter).
The only down side of the high flows is that they came a little too
late. As was stated the flows didn't increase until May 23rd. Up
until May 6th the flows had been held at 1,900 cfs but since runoff
had not started and the reservoir water level was dropping markedly,
the Bureau of Reclamation cut the flows in the river to 1,500 cfs.
What Ken Frazer fears is that the 17-day hiatus probably killed many
of the sac brown trout fry that were still in the gravels. The fry remaining
in the gravels that were dewatered or suffering diminished flows hence
diminished oxygen levels were undoubtedly lost. How large a percentage
of the year class of 2008 is a moot question, suffice it to say that fifty
percent loss is optimistic and seventy-five percent is more realistic.
With Bighorn Reservoir completely full (it is now one foot into the
flood pool and inflows exceed outflows by 2,000 cfs) the flows should
continue to be above recommended minimum flow of 2,500 cfs for at
least a month, maybe two months. While there is plenty of water in the
river and the reservoir now is the time that a sound water management
plan can be worked out between the people using the reservoir and the
people using the river.
While the water is up in the river, it is extremely clear. The
nymph fishing has been quite productive. A standard array of
sowbugs, San Juan worms, scuds, a red midge larva patterns
has been very good. The dry fly fishing has been slow, but there
are still blue-winged olives hatching on cloudy days and the pale
morning duns and black caddis should start appearing any day now.
To top it off, the heavy crowds that crammed the river in April,
May and early June have tapered off. High gasoline prices have
deterred a few people from making long trips. While the out-of-state
license plates have diminished the local license plates have remained
about the same. Still it is possible to float the river and encounter
only a handful of boats.
Most of the good fishing spots are producing well, but the trout maybe
holding lower in the pools—more trout are concentrated where the
pools tail out rather than at the head end of the pool. Also, at the
bottom end of an island where the flows start to intersect is another
place to fish. Islands that are now submerged hold fish where the
water drops off the edge. Side channels that were dry for nearly a
decade hold trout now, but the submerged willows, grass, and Russian
olives make for difficult presentations.
If you can find the time, you should try the Bighorn at high flows,
I'll bet that you will find that the fishing is some of the best you have ever experienced.
Bob Krumm
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