EAGLE – Downstream from where Eagle Road crosses the Boise River, a faded piece of pink flag hung from a shrub by the river, marking a significant spot.
A group of Boise Valley Fly Fishers volunteers placed the ribbon there last fall to indicate the presence of a brown trout nest, or nesting site where the fish lay their eggs. The group marked 200 redds along a 16-mile stretch of the Boise River as part of a partnership with the local flood control district, Boise River Flood District No. 10, to protect the sites during the District winter flood control maintenance activities.
The Boise River has a number of dams for irrigation and flood control. However, the river needs annual maintenance, carried out by the flood control district, to remove objects that could cause flooding, usually trees that could cause flooding if overturned, or logs. But that job requires maneuvering heavy equipment in the river, which can damage fish habitat if operators don’t know which spots to avoid, a press release on the project said.
Marking brown trout spawning grounds and meeting with contractors to share spawning ground locations helped protect 99% of them, Boise Valley fly fisherman conservation manager Troy Pearse said during an interview. an event to reward the flood control district for its efforts. Also, tagging the redds didn’t cost any extra money, he said.
The project took place on the stretch of river between Willow Lane Park in Boise and Star, according to the release.
Brown trout are a favorite of local anglers, Pearse said. It spawns in November when the river is generally at its lowest flow and water level, he said. Although the fish is not native to the river and has been stockpiled, this practice has largely ceased, he said.
To find the redds, the volunteers had to float down that stretch of the river multiple times, Pearse said. A single brown trout nest is about the size of a hoop, he said. From the surface, the gravel in this area appears cleaned and lighter in color compared to the surrounding riverbed, he said. Volunteers marked areas where multiple spawning grounds were grouped together, placed biodegradable flags on either side of the river from the site, created a GPS waypoint and took a photo of the river there to share with teams. of maintenance.
The flood control district hopes to expand the project in future years to protect brown trout spawning habitat, said district manager Mike Dimmick. It’s part of a new effort to preserve and enhance habitat value while controlling flooding, he said.
After the spring flooding that followed 2017’s “Snowmaggedon,” the district struggled to secure funds for flood recovery, Dimmick said. District officials were able to ask the Idaho Legislature to create a $1 million fund for flood mitigation projects, he said. Projects so far have included partnering with the U.S. Army Corps of Engineers to create a state-of-the-art two-dimensional map of the river that will guide decision-making on what flood control projects to do, a-t -he declares.
The district will also develop a “gravel management plan” to improve habitat in the river, Dimmick said. Many species of fish need a certain size of gravel — usually the size of a marble golf ball — in which to lay their eggs, Pearse said. The eggs will settle between pieces of gravel of this size, allowing them to remain protected from predators and avoid being washed downstream.
In an undammed river, rocks of all sizes would be “conveyed” together down the river, Pearse said. But damming a river traps gravel behind the dam, preventing it from moving downstream, Pearse said.
“Over time you’re stripped of those little gravels,” Pearse said, “really all that’s happening is bank erosion,” he said.
Adding gravel to the river system can improve the quality of fish habitat, ensuring the survival of more fish, Pearse said. Idaho Fish and Game collects data on the number of baby fish, or fry, that emerge each season, he said. Populations tend to be higher in areas where gravel has been added to the river, he said.
So far, one project added gravel to the river in January 2021 near the Glenwood Street Bridge, Pearse said. Boise Valley fly fishers plan to monitor the success of this project and work to protect spawning grounds in this area in partnership with the district, he said.
Even tree removal as part of flood control is now being considered more carefully, Dimmick said. Trees and other vegetation provide good habitat for fish by providing shade, which keeps the water at an optimal temperature. It also provides cover from predators. Now, instead of removing any tree from the river that leans at a certain angle, maintenance crews are working to keep the trees in place, Dimmick said. There are also projects underway to move trees and logs to where they are less likely to cause flooding and to anchor them, which can also improve fish habitat, Dimmick said.
Individuals too can make a difference by working to protect the river and its fish, Pearse said. There are concerns that as local towns grow and more people enjoy fishing on the river, it could decrease the trout population, Pearse said. To ensure that everyone had the opportunity to enjoy catching brown trout, he encouraged the practice of catch-and-release.