Flood #10 partners with Boise Valley Fly Fishers to enhance trout habitat in Boise River

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Media contact: Steve Stuebner, 208-484-0295, [email protected]  
Boise Valley Fly Fishers: Troy Pearse, 208-870-1025, [email protected]
Flood #10: Mike Dimmick, District Manager, 208-861-2766, [email protected]

GARDEN CITY (Friday, March 3, 2023) – Volunteers with Boise Valley Fly Fishers have been working together with Flood Control District #10 to enhance trout habitat in a side channel of the Boise River, adding small gravel ideal for spawning and creating hiding cover with woody material.

Recent trout fry surveys by the Idaho Department of Fish and Game shows the fish-enhancement work is yielding significant results. In the surveys, IDFG found more trout fry in the New Dry Creek side-channel – about 85 brown and rainbow trout fry – than any other surveyed location in the Boise River.

The other areas surveyed featured about 20 trout fry in other surveyed locations in the Boise River.  

“Hands down, Idaho Fish and Game found more trout fry in that side channel than any other place in the river,” said Mike Dimmick, Flood #10 project manager. “The New Dry Creek side channel is a working well as a “test plot” where we can experiment with gravel placement and woody material to see how things are working.”

“That site is one of the most productive areas in the Boise River,” added Troy Pearse, conservation director of BVFF. “It’s good evidence that our work is showing positive results.”

About 10 volunteers with Boise Valley Fly Fishers recently worked together with Flood #10’s contractor to spread 15 cubic yards of gravel in the side channel next to the New Dry Creek diversion, downstream from the Glenwood Bridge. Sun Roc in Eagle donated the gravel as a project partner. 

BVFF volunteers and the contractor placed the gravel in the upper end of the side channel to allow the river currents to spread out the gravel downstream when the river rises this spring. Last year, BVFF and Flood #10 placed about 12 yards of gravel in the same side channel, and anchored some woody material along the river bank to provide a place for trout fry to hide from predators during the winter months. This is the third year of gravel-augmentation work.

Pearse said there are three essential ingredients needed to produce more naturally spawning brown and rainbow trout in the Boise River:

  1. 1. Woody material hanging over the river bank for trout fry to use as hiding cover. That helps the fry survive the first few months of their lives without getting taken by predators such as other fish, birds and river otters.
  2. 2. Side channels with perennial stream flows are ideal locations for spawning. Fish don’t survive as well in the main channel after emerging from eggs as fry, he said.
  3. 3. Ideal spawning gravel (1/2-inch to 2-inch round) for trout to dig nests and spawn. With Lucky Peak, Arrowrock and Anderson Ranch dams absorbing sediment and small gravel from mountain streams above, that reduces the deposition of spawning gravel in side channels of the Boise River, he said. 

The lack of woody material in other side channels has been a limiting factor, Pearse said. As a result, there has been poor over-winter survival in those areas.

In addition to the side channel enhancement work, BVFF once again pin-flagged brown trout redds in the Boise River channel to mark them for Flood #10’s winter maintenance contractor so those spots can be avoided. The fly fishing club has been monitoring 50 sites between Willow Lane Park and Star for brown trout spawning. This year, they counted and marked 130 brown trout redds.

“That’s important so our winter maintenance crew can see where the trout redds are, and it’s easy to avoid them,” Dimmick said.

BVFF also has mapped the trout redds and provided maps to Flood #10 as an additional guide.

Working together with BVFF on the fish-enhancement activities is something Flood #10 can do while working on winter maintenance activities. “We donate some of our contractor’s time and equipment when we’re on site,” Dimmick said. “Scheduling the gravel work when we have our equipment operating in those locations makes it pretty quick and convenient.”

Flood #10 also thinks about how to preserve woody material near the bank of the Boise River in terms of preserving a root wad or tree limbs next to the bank, while removing the bulk of a tree that’s fallen into the river to keep the channel open, he said.

Last year, BVFF and IDFG presented a plaque to Flood #10, commending them for the first year of trout-enhancement partnership work. 


Brown Trout fry discovered in side channel during IDFG survey on Boise River (courtesy BVFF)
Boise Valley Fly Fishers volunteers spread the gravel into the upper end of the side channel. Higher water this spring will distribute the gravel in the lower side channel through natural means.
Photo of newborn fry thriving under woody winter cover on the banks of the New Dry Creek side channel. (courtesy BVFF)

For more information about Flood Control District 10, contact Mike Dimmick, District Manager [email protected](link sends e-mail)
For feedback on the stories, contact Steve Stuebner [email protected]

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