Two hydroelectric dams built on the Elwha River in Washington state between 1913 and 1927 blocked Pacific salmon migration for nearly a century, until their demolition between 2011 and 2014 reopened 113 kilometers of the river to fish that had been shut out for generations, according to the US National Park Service (NPS) and the National Oceanic and Atmospheric Administration (NOAA).
For thousands of years, Pacific salmon swam up the Elwha River from the Strait of Juan de Fuca into the mountains of the Olympic Peninsula to spawn. That ancient cycle collapsed in the early 20th century after Canadian businessman Thomas Aldwell built two hydroelectric plants to supply power to the city of Port Angeles, the NPS said.
The dams reduced the habitat accessible to migratory fish to just eight kilometers, or about five miles, of river channel, according to NPS data. After the structures came down, Chinook and coho salmon quickly recolonized stretches of river that had been off limits for generations, while the sudden release of sediment revitalized the estuary and the surrounding coastline, NOAA said.
How Aldwell's dams reshaped the Elwha River
Aldwell began buying land along the river in 1910 with financial backing from investors in Chicago. The first dam collapsed at its foundations in 1912, but a rebuilt plant began operating in 1913, supplying power to a pulp mill in Port Angeles and helping drive the region's timber industry, the NPS said.
Aldwell disregarded an 1890 law requiring passages for migrating fish, according to the NPS timeline for Olympic National Park. As compensation, authorities built a fish hatchery next to the dam in 1915, but it failed and was abandoned by 1922, leaving sea-run salmon stranded in front of a concrete wall 32 meters high.
As demand for electricity grew, construction began in 1925 on a second dam, Glines Canyon, which started operating in 1927 standing 64 meters tall. Together, the two dams powered the local economy but blocked more than 90% of the watershed available to salmon and other fish that migrate between rivers and the ocean, and they also affected sites of cultural and religious importance to the Lower Elwha Klallam community, the NPS said.
The Lower Elwha Klallam Tribe's decades-long campaign
The Lower Elwha Klallam Tribe, a Native American nation whose traditional territory covers the Elwha River watershed on the Olympic Peninsula, spent decades pressing for the dams' removal alongside environmental groups. Their campaign helped secure passage of the Elwha River Ecosystem and Fisheries Restoration Act in 1992, which authorized the US Department of the Interior to buy the dams and restore the river's natural state.
Demolition work began in September 2011. The first dam was gone by 2012, and removal of the Glines Canyon dam was completed in August 2014, according to the NPS.
Salmon returned before the work was even finished
The biological response began before demolition was complete. Hundreds of Chinook salmon swam past the site of the old barrier in 2012 and spawned in channels that had been inaccessible for nearly a hundred years. Once both dams were gone, coho salmon, pink salmon and steelhead trout also returned to the river. NOAA said aquatic organisms had regained access to the entire river.
The reconnection also released sediment and driftwood that had built up behind the reservoirs for decades, materials that are essential for forming beaches, spawning grounds and estuaries downstream.
A limited tribal fishery returns after 2024
A decade after the dams were fully removed, the coho salmon population had grown enough that authorities approved a limited tribal fishery for ceremonial and subsistence purposes in 2024. Olympic National Park said the return of fish to the river's upper reaches has turned the Elwha into a natural laboratory for studying how rivers recover once dams are removed.
