The Lower Boise River runs from Lucky Peak dam to the Snake River and the upper section (from the Dam down to Star) has a good population of naturally reproducing rainbow and brown trout. Lucky Peak is a tailwater dam, which helps keep the waters cool in the summer, but three common issues below a dam in an urban area that can limit wild trout reproduction are: 1) Lack of spawning size gravels; 2) Loss of side channels; and 3) Lack of Large Woody Debris.

GRAVEL AUGMENTATION

The Boise River has lost much of its spawning size gravels which limits where wild brown and rainbow trout can spawn. Two winters ago, Boise Valley Fly Fishers (BVFF) worked with Idaho Fish and Game (IDFG) and Boise River Flood Control District #10 (FCD 10) Boise Flood to improve trout spawning and rearing habitat on a side channel of the Lower Boise River in Garden City. We worked with IDFG to identify areas that had suitable depth and flow for rainbow and brown trout spawning and added a total of 12 cubic yards of gravel to three areas in the side channel. We timed adding the gravel when BFlood10 was in the area doing their annual winter stream maintenance work and they donated time and machinery to move the gravel into the side channel where our volunteers raked it into place.  For more details on the gravel augmentation, see these articles by the Idaho Statesman and BREN.

LARGE WOODY DEBRIS

Woody debris provides refuge for trout fry and is critical to the survival of young trout. However, flood control practices in urban areas like Boise remove fallen trees to reduce flood risk. We have been fortunate to be able to work with FCD 10 and they agreed to reposition and retain some fallen trees in this side channel as an experiment to improve trout habitat. We appreciate FCD 10’s extra efforts to improve woody debris when possible.

SIDE CHANNELS

Side channels are the best place for trout spawning and rearing. They have reduced flows that are conducive to trout spawning and tend to have the right depth and structure for trout to make their redds. Side channels with year-round flow are the most valuable because they provide opportunities for Brown Trout to spawn in November and they give young trout fry shelter to survive their first winter. BVFF’s side channel has flow year-round, although the entry sometimes gets clogged with rocks and logs placed there by the public to cross, which reduces inflows and blocks fish passage. Please help us keep side channels flowing and do not block them off.

SPAWNING

Because of the extended drought, the BVFF side channel has had lower than average flows, but we have seen rainbow trout redds in the spring and brown trout redds in the fall in the areas where we added gravel. A recent review of the gravel we placed in the stream two winters ago shows that the gravel at the head of the channel is making its way down the side channel from higher flows during spring runoff and mother nature is using it to make a new spawning area, which brown trout used this fall to spawn. The gravel at the top of the side channel is getting thin and we are working on refreshing it this winter or next winter.

FRY SURVEY

This Fall we were able to accompany IDFG on their annual Lower Boise River trout fry survey and see firsthand how the habitat improvements were working.

I am very pleased to report that we found dozens and dozens of brown and rainbow trout fry in the side channel!

Most of the trout fry were located in the large woody debris, which underscores the importance of woody debris. IDFG Fish Biologist Tim D'Amico, who led the fry survey, was very impressed with the number of trout fry in our side channel and commented that it was one of the most productive spots they had sampled that year.

RECIPE FOR SUCCESS

A side channel that flows year-round, plus spawning size gravel and woody debris is winning trout habitat combination to improve the trout population. BVFF has adopted this side channel and we plan to continue to work on habitat improvements as well as do regular river cleanups in the area. We are talking with IDFG about the potential to restore year-round flow to other side channels that have become dry over the winter—something that would continue to improve the wild trout populations in the Lower Boise River.

Another critical factor for success is the partnerships between BVFF, IDFG and FCD 10, working together to improve and protect trout habitat on the Lower Boise River. And we couldn’t do it without the support of our members and volunteers.

We are raising money to do additional gravel augmentations.  Please buy a "Greenback" from the BVFF store to help support our efforts to increase trout spawning in the Boise River.

HABITAT SIGNS

BVFF added a trout habitat sign to the side channel to help educate people about the importance of side channels and the lifecycle of brown and rainbow trout. Since then we have added similar trout habitat signs at the Diane Moore Nature center as well as the first anti-litter sign on the Lower Boise River!

THANKS

Our thanks to all of our project partners and volunteers that made this project happen.

• IDF&G and BioAnalysts who helped us plan the gravel augmentation
• Boise Flood District 10 who helped move the gravel into the river
• Sunroc for donating the gravel
• FFI for funding the Trout Habitat Sign