Every year, hundreds of Chinook salmon make their way up the Willamette River to Fall Creek Lake. In 2010, the fish population in the waters outside Eugene, Oregon, largely came from hatcheries. Today, with help from the U.S. Army Corps of Engineers’ Willamette Valley Project, there is now a self-sustaining wild salmon population.
The change is the result of a regionwide effort to leverage hydropower and other resources to benefit fish and energy production.
“The whole region is really working on trying to improve the status of endangered fish species,” says Greg Taylor, supervisory fisheries biologist with the project. “The U.S. Army Corps of Engineers is looking out 30 years and thinking—and then implementing—a whole host of projects. The biggest picture ones are in the arena of downstream fish passage. But that is a huge challenge, with big costs and a lot of uncertainty.”
The Corps’ focus is endangered fish species, such as Chinook salmon, steelhead and bull trout. The Corps helps fish migrate up and down rivers with the goal of repopulating fish above dams, helping them live full life cycles and potentially helping them be successful enough to be removed from the endangered list.
Hydroelectric facility management significantly influences fish health. Management strategies can help fish migration, regulate water temperatures and manage levels of dissolved gas, all crucial factors for fish survival.
The salmon in Fall Creek Lake face many of the challenges hanging over fish throughout the Pacific Coast. Salmon do best in cooler waters with higher flow rates. Waters throughout the region have warmed, and Fall Creek Lake has always had a drier basin—meaning lower, warmer water.
“It’s just a tough place to be a salmon,” Greg says.
In 2010, the Corps began a practice Greg says has greatly benefited the area’s salmon: annual drawdowns of Fall Creek Lake. Some dams, such as Fall Creek Dam, have submerged passages that allow fish to swim safely through them. Many species of Northwest fish tend to stay in the top 50 feet of a body of water. The Corps can lower water levels behind dams to help fish find these safe passages and improve their survival rates.
At other facilities, more water is released through spillway gates, which is shown to help fish pass safely downriver. Each facility and ecosystem are unique, so the challenges differ along the Willamette, McKenzie and Columbia rivers.
“You can’t just do what you did at Fall Creek and replicate it over in the McKenzie,” Greg says. “It’s got to be a tailored and custom solution in each situation.”
After the fish have moved past a dam, hydro facilities play important roles in managing water quality. Spilling water through spillway gates helps fish migration, but it also increases dissolved gas levels, which can be harmful to fish. Hydroelectric generators don’t add dissolved gas to water, so running generators while also spilling water can help balance gas levels.
Additionally, dams can introduce cooler water downriver. Shallower river water warms in the summer heat, while deeper water in reservoirs is often colder. Running additional water through generators at specific times can ensure fish have the cooler waters they need during migration season.
Greg and his team evaluate how decisions could impact different fish populations—and different parts of the same population. For example, if the Corps’ goal was just to help Chinook salmon reach a reservoir as they migrate upriver in the spring, dams could spill a huge amount of water, lowering temperatures for migration. But that would warm the reservoir and hurt juveniles rearing in the reservoir. It would also impact river temperatures later in the year and increase the amount of suspended sediments in the water.
“You can’t get the blinders on and just think about one aspect of the life history of these fish,” Greg says. “You’ve got to think it all the way through and think about how it’s going to affect all aspects of that fish, or your other authorized purposes.”
The Corps also helps fish migrating upriver. Fish ladders aren’t available at every facility to help fish migrate past the dam. A couple of times a week, biologists with the Corps head out to the river to help move tens of thousands of fish.
At five different facilities along the Willamette River, fish are directed into ladders that lead them into holding pens—basically oversized swimming pools. The fish then follow a spray of water and jump into a flume, where biologists inspect each fish. The Corps and Oregon Department of Fish and Wildlife have a disposition plan that determines how many of which species will be moved above dams and which will be sent back into the river below. The fish moving above the dam get loaded into trucks that drive them upriver.
Every fish a biologist works with is counted, and for target species, data such as sex and length are tracked. Biologists also collect a small tissue sample for parentage analysis. By looking at genetic data, they can determine whether its parents had previously been tracked and ascertain whether the fish had spawned above the dam.
“It’s a really good big-picture way to understand how we’re performing,” Greg says. “If you put 500 fish up there, and you get 100 back, you haven’t improved the status of the population. So, the big-picture goal is for that population to sustain themselves.”
While the salmon at Fall Creek Lake have begun sustaining a stable population level, that’s not true in all bodies of water the Corps works with. But Greg and his team are working hard toward that goal.
“Some of these fish feel like my fish children, for sure,” Greg says with a laugh. “They keep me up at night. I worry about them.”