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South Fork flows to jump next week, for post-fire fish habitat restoration

Flows in the South Fork of the Boise River will jump next week as part of a project to recover fish habitat in areas impacted by heavy sedimentation after last year's Elk and Pony Complex fires. Idaho Fish & Game reports that the river's volume from Anderson Ranch Reservoir will rise by 400 cubic feet per second on Monday, and another 300 cfs Tuesday, then remain at 2,400 cfs for eight days; by Aug. 29, the flows will drop back to 1,700 cfs.

A multi-agency team developed the project to mimic spring runoff, which normally would help clear out sediment and debris after fires; flows in the South Fork of the Boise are regulated by dams that store water for irrigation and flood control, so that didn't just naturally happen. The idea is to do it now at a time when water is available; Fish & Game, the Forest Service, the U.S. Bureau of Reclamation, the University of Idaho and Trout Unlimited all are cooperating in the project. Click below for a full announcement from Fish & Game.


“To Preserve, Protect, Perpetuate and Manage”


Contact: Idaho Fish and Game 208-334-3746

For Immediate Release


Water Managers Raise South Fork Boise to Help Fish

Water managers will increase flows in the South Fork Boise River next week in an effort to restore fish habitat damaged by last year’s wild fires. The Bureau of Reclamation will increase the river volume from Anderson Ranch Reservoir by 400 cfs (cubic feet per second) on Monday August 18, and again on Tuesday by another 300 cfs.  The flow will remain at 2,400 cfs for eight days. By August 29 the flow will return to 1,700 cfs.

This window of high water will help recover fish habitat in the South Fork Boise River, one of Southwest Idaho’s most important trout streams. This river not only supports critical habitat for migratory bull trout, it is also Southwest Idaho’s premier rainbow trout fishery.

Habitat changed significantly when the Pony and Elk Complex fires burned hillsides along the river last summer. Intense rain from thunderstorms followed by snowmelt saturated the exposed soils, causing several large mudslides to flow into the river, damaging roads and stream habitat.

Large volumes of sediment and debris can dramatically change fish habitat. Fine sediment fills in pools, side channels and small spaces between cobble stones, which are important winter habitat for small fish. Sedimentation also reduces the abundance and diversity of the insects that fish eat. On the positive side, debris can add new spawning gravels and woody debris, both important for producing young fish and creating cover where fish hide. While fish populations may decline shortly after mudslides, they usually rebound in the long-term; benefiting from added nutrients, gravels and woody debris.

Debris flows into Idaho’s rivers are common after fires. In naturally flowing rivers, fish habitat improves quickly as high spring runoff moves sediment and debris downstream. In regulated rivers like the South Fork Boise, dams store water for irrigation and flood control, inhibiting peak flows. 

A multi-agency team developed recommendations to increase flows next week to mimic spring runoff, helping to restore habitat in the South Fork Boise at a time when water is available. Staff from the US Forest Service, US Bureau of Reclamation, University of Idaho, Trout Unlimited and the Idaho Department of Fish and Game cooperatively developed the strategy to provide a pulse of high water to benefit fish and insect communities in the river.



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Betsy Z. Russell
Betsy Z. Russell joined The Spokesman-Review in 1991. She currently is a reporter in the Boise Bureau covering Idaho state government and politics, and other news from Idaho's state capital.

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