Lewis River Fish Passage Reopens 117 Miles to Salmon

Estimated reading time: 6 minutes · Last updated: 30 October 2026

Salmon and steelhead on Washington's Lewis River now get past three hydroelectric dams by truck. PacifiCorp's Lewis River fish passage network on the Swift, Merwin and Yale dams traps adult fish at a collection facility and drives them above Swift Dam to spawn. A floating collector in Swift Reservoir gathers young fish and carries them back down to the lower river. The programme has reopened 117 miles of historic upstream habitat. Construction began in April 2011, and the system was fully running in 2012. The 510-megawatt hydropower complex stayed in place throughout. That matters because Washington leans on its dams for clean power, and tearing them out would open a gap in supply.

How Adult Salmon Ride a Truck Past Three Dams

The upstream half of the system begins at the Merwin Upstream Collection Facility. A collection facility is a structure built to gather migrating fish in one place so they can be moved around an obstacle. At Merwin, a steady flow of water draws returning adults away from the turbines and into ladder traps. There they are held instead of being left to search for a route that no longer exists.

Crews then sort the catch, load the fish onto trucks and drive them to water above Swift Dam. The adults are released there to spawn without further help, in stretches of river that had been out of their reach. In effect, the trucks replace a climb that the concrete made impossible.

Moving fish by road lets a single collection point serve a migration route that crosses three dams. The approach treats the Swift, Merwin and Yale dams as one barrier to be bypassed rather than three separate engineering problems. Each fish makes one trip by truck instead of tackling a series of structures on its own.

How the Floating Surface Collector Gathers Young Fish

Juvenile salmon heading out to sea face the same barriers in reverse. Swift Reservoir replaced a moving river with still water, so young fish lose the current that would otherwise carry them downstream. The Floating Surface Collector in Swift Reservoir addresses this by generating an artificial flow that mimics the pull of a river heading downhill.

Nets steer the juveniles toward the floating structure, and the fish are collected inside it. They are then trucked to the lower river and released below the dams. That completes a journey the reservoir would otherwise have stalled.

Both facilities were still moving migrating fish in October 2026, about 14 years after the network became fully operational in 2012. Together they run a two-way transport programme for native salmon and steelhead. Adults are carried up to spawning water and their offspring are carried back down. The combined result is the 117 miles of historic habitat now open to fish again.

What a Century of Dam Building Did to Northwest Rivers

Hydropower drove much of American industrial growth in the twentieth century. By the 1940s it supplied up to 40% of all electricity generated in the United States. That gave cities and factories cheap, plentiful power and steadier grids. Federal and private builders turned free-flowing rivers into dependable generating corridors, and their output fed the post-war boom.

Washington leaned on hydropower especially heavily. The state produces more than 25% of the country's hydroelectric power, and river dams supply upwards of half the electricity its own residents and businesses use. That reliance has kept its power rates low.

The rivers paid the cost. Fast, cold Pacific Northwest streams became slow, warm reservoirs, and the dams cut off the routes migrating fish used to reach spawning grounds. Habitat access shrank over the past century, and wild salmon and steelhead numbers have fallen by more than 90% in several basins. That decline is the problem the Lewis River work was built to address.

Why Washington Is Fixing Dams Instead of Removing Them

Demolition can look like the most direct way to bring fish back. Anke Maree, a staff writer at Energies Media, argues it is not realistic in Washington, where large dams anchor the power supply. Taking them out, she writes, would leave a shortfall that intermittent generators could not cover straight away. Intermittent generators are sources whose output rises and falls with conditions.

State law sharpens the point. Washington's Clean Energy Transformation Act requires a 100% carbon-free electric grid by 2045. Maree's case is that without the big hydroelectric dams, utilities would have to turn to fossil fuels to meet peak demand, which would push that target further out of reach.

The Lewis River system shows the alternative in practice. The 510-megawatt complex in southwest Washington kept generating while passage was added around it, with construction starting in April 2011. Maree presents it as a model for other ageing hydropower fleets. Still, the 117-mile figure measures habitat reopened, not fish recovered. How many salmon and steelhead are actually returning is a separate question the habitat number does not answer.

Can collection and trucking restore Lewis River fish runs?

The bottom line

The Lewis River fish passage is a working answer to a hard trade-off. PacifiCorp kept a 510-megawatt hydropower complex running and built a route around it. Adults heading upstream go through ladder traps and onto trucks, and juveniles heading downstream go through a floating collector and onto trucks. The result is 117 miles of historic habitat back within reach of salmon and steelhead. The open question is what that habitat yields. Reopened river miles are a precondition for recovery, not proof of it. The real test is whether returns rise in a region where several basins have lost more than 90% of their wild fish. With a 2045 carbon-free deadline, Washington needs both its dams and its rivers.

What to watch

• Watch for published counts of adult salmon and steelhead using the 117 miles of reopened habitat above Swift Dam; no date has been set for such figures.
• Watch Washington's progress toward the 2045 deadline under the Clean Energy Transformation Act, where Maree argues large dams are needed to meet peak demand without fossil fuels.
• Watch whether other ageing hydropower operators adopt collection-and-trucking passage modelled on the Lewis River system; no date has been set.