South Fork Boise River

Winter on the South Fork Boise.  It is usually a time for the most dedicated anglers, but mostly quiet.  So this website will fill some time with a few science reports that we’ll strip out over this month.  We’ll call it Science February.

“The river was cut by the world’s great flood and runs over rocks from the basement of time. On some of those rocks are timeless raindrops. Under the rocks are the words, and some of the words are theirs.  I am haunted by waters”

When Norman Maclean penned those words in the immortal novella A River Runs Through It, he referenced the Big Blackfoot and the Clark Fork Rivers of Montana.  The world’s great flood referenced the break of the ice plug that held back Lake Missoula, draining the lake, creating the channeled scablands of eastern Washington, and depositing sediment in the Willamette Valley of Oregon.  But whose “words are theirs” the words found under the rocks?

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The South Fork Boise River flows into Arrowrock Reservoir some 21 river miles downstream of the Danskin Bridge.  Arrowrock also gets water from the Middle and North forks of the Boise River.  These three branches form three major avenues of access for fish that wander from headwaters to mainstem rivers.  And the rare bull trout is known to migrate great distances, sometimes hanging out in the South Fork Boise, only to drift back downstream to Arrowrock Reservoir and then travel up to a headwaters stream tributary to the North or Middle Fork Boise River.

Understanding the effects of Anderson Ranch Dam and Arrowrock operations on bull trout is an area of inquiry that the Bureau of Reclamation has pursued for many years.  Original studies in the late 1990s and early 2000s helped establish an understanding when the bull trout move between the headwaters and Arrowrock reservoir.

In  the fall of 2011 more field work was initiated and a weir was placed in the North Fork Boise River at Barber Flats and a similar structure on the Middle Fork Boise River.  The Bureau has received assistance from Idaho Fish and Game and the Boise National Forest.  The bull trout captured at the weirs are implanted with a radio tag and are tracked for two or three years to better understand living and migratory habits. Continue Reading…