After the Elwha River’s two concrete dams came down, estimated average annual Chinook returns rose from 2,827 fish to 4,734, while the share taken for hatchery broodstock fell from 53 per cent to 31 per cent. More adults remained in the river to cut nests into gravel that salmon had been unable to reach for a century.

The headline numbers describe a striking before-and-after change, but they do not describe a purely wild run. Most returning Chinook were still hatchery-origin fish, and the estimates before and after removal were produced with different counting methods.

For a century, the Elwha stopped at concrete. Elwha Dam stood about eight kilometres from the Strait of Juan de Fuca, while Glines Canyon Dam blocked the river farther upstream. Neither structure had facilities that allowed salmon to pass.

Crews began taking the dams apart in September 2011. Elwha Dam was gone by April 2012, and removal of Glines Canyon Dam was completed in 2014. The river then ran freely from the Olympic Mountains to salt water for the first time in more than a century.

Two dams that held a century

The Elwha drains 833 square kilometres and flows for 72 kilometres from its mountain headwaters to the Strait of Juan de Fuca. The dams eliminated access to about 95 per cent of the watershed for ocean-going fish.

Elwha Dam was built at river kilometre 7.9 and completed in 1912, creating Lake Aldwell. The 64-metre Glines Canyon Dam was completed at river kilometre 21.4 in 1927, creating Lake Mills. Together, the walls left returning salmon with only the lowest portion of the river.

The damage was cultural as well as ecological. The dams flooded historic homelands and cultural sites belonging to the Lower Elwha Klallam Tribe, while blocking fish that had supported the community for generations. The tribe’s restoration overview describes dam removal as only the beginning of a much longer effort to recover the watershed.

In 1992, Congress passed the Elwha River Ecosystem and Fisheries Restoration Act. The law authorised federal acquisition and removal of both projects when removal was found necessary for restoring the ecosystem and native anadromous fisheries.

After nearly two decades of planning, demolition began on 17 September 2011. The National Park Service identifies the project as the largest dam removal in United States history at the time. A rockfall below the former Glines Canyon site created another fish barrier in 2014, but crews finished clearing it in September 2016.

The reservoirs had accumulated nearly 30 million metric tonnes of sediment. A five-year USGS sediment analysis found that about 65 per cent eroded, with roughly 90 per cent of the released material reaching the coast and expanding the delta by about 60 hectares. Terra Daily followed the same process while scientists were tracking where the stored sediment would go.

Nests, then machines that listened

The pre-removal and post-removal Chinook estimates did not come from the same instrument. From 1986 through 2010, surveyors counted redds, the gravel nests in which Chinook lay their eggs, throughout the accessible lower river. They then converted those observations into estimated run sizes using 2.5 fish per redd and other adjustments.

That method became difficult when dam removal filled the water with suspended sediment. From 2012 through 2020, researchers instead used two multibeam sonar units near the mouth, one for each channel into which the river divided. The instruments produced moving acoustic images of fish swimming through the river cross-section.

The 2024 study by George Pess and ten colleagues calculated an average annual return of 2,827 Chinook before removal, with a standard deviation of 1,778. Sonar produced averages of 3,444 during removal from 2011 through 2014 and 4,734 after removal from 2015 through 2020.

The estimated number remaining to spawn naturally rose from an annual average of 1,393 before removal to 3,523 afterward. At the same time, the proportion removed for hatchery breeding fell from 53 per cent to 31 per cent. That meant a smaller share of a larger return entered the hatchery.

The comparison still needs care. Redd expansion and sonar are different estimation systems, and the study evaluated a package of dam removal, hatchery production, fishing restrictions and active relocation. The figures establish that estimated returns were higher in the post-removal period, not that dam removal alone produced every additional returning adult.

A hatchery run spawning in open water

The returning Chinook population remained overwhelmingly hatchery-origin. Across 2009 through 2020, the median hatchery-origin proportion was 95.9 per cent, with annual values ranging from 92 to 98 per cent. Even among Chinook spawning naturally in the river, the median hatchery-origin share was 93.8 per cent from 2016 through 2020.

That distinction matters because a fish can begin life in a hatchery and later spawn naturally in a river. Terra Daily has covered how hatchery fish can make a spawning population look wilder than it is. On the Elwha, “naturally spawning” therefore cannot be treated as interchangeable with “wild” or “natural-origin.”

The Elwha Chinook hatchery programme began in 1930 using Elwha River stock. Researchers concluded that it helped preserve the river’s distinctive genetic lineage while the dams blocked most of the watershed. Before removal, the hatchery released an average of approximately 2.6 million juvenile Chinook each year.

The increase in returning adults was still largely a hatchery story. The study attributed much of the variation during and after removal to hatchery production and the survival of hatchery-reared juveniles at sea. Median smolt-to-adult return rates increased for both hatchery-origin and natural-origin Chinook during the removal period, although the values varied widely from year to year.

Managers also helped fish enter the newly opened river. In five of the ten years during and after removal, surplus adult hatchery Chinook were relocated to sites above the former Elwha Dam. Other fish reached the new water without assistance, and redd surveys documented Chinook in the middle river immediately after the lower dam disappeared.

Once the Glines Canyon rockfall was cleared, Chinook nests were repeatedly found above the former upper dam. The most heavily used upper-river spawning area was the channel through the former Lake Mills reservoir. Across surveyed years, the distance between the lowest and highest recorded redds stretched roughly 45 to 55 kilometres.

Natural-origin juveniles began leaving the river in much larger numbers after the sediment pulse eased. A separate analysis of juvenile Chinook out-migration documented the early life-history changes, while the adult-response study estimated more than 500,000 natural-origin subyearlings in 2019 and almost one million in 2020.

Those juvenile surges were real, but they had not yet produced a self-sustaining adult population within the study period. Estimated productivity among naturally spawning Chinook remained at or below 0.40 returning adults per parent in every brood year examined. Replacement requires a value of one.

Steelhead entered the river differently

Winter steelhead also expanded after the dams came down. Sonar estimates from 2014 through 2020 ranged from 890 to 1,985 returning adults, with an annual average of about 1,400. Hatchery-origin steelhead contributed substantially to the larger lower-river returns.

Farther upstream, the balance changed. Samples collected above the former Elwha Dam contained a much higher proportion of natural-origin winter steelhead than samples from the lower river. Researchers concluded that the upstream expansion was driven predominantly by natural-origin spawners.

Summer steelhead had become extremely scarce before and during removal. Snorkelers saw one adult in 2013 and six in 2016 during limited surveys. When teams began surveying the same 23 kilometres of middle and upper river each September, they counted 74 fish in 2017, 216 in 2018, 318 in 2019 and 92 in 2020.

Less than one per cent of those summer steelhead carried the clipped adipose fin used to identify hatchery fish. Researchers concluded that part of the returning run probably developed from resident rainbow trout that had survived above the dams and regained access to the sea. The same species had persisted in two forms on opposite sides of the concrete.

A broader USGS riverscape study compared snorkel surveys conducted in 2007 and 2008 with surveys in 2018 and 2019. Divers counted 54,616 Chinook, bull trout, steelhead, rainbow trout and coastal cutthroat trout across 22 matching reaches spanning 65 river kilometres. After removal, Chinook densities in some middle reaches exceeded those recorded anywhere in the lower river before the dams came down.

A free river, not a finished run

A broad fishing moratorium remained in effect from 2012 through the summer of 2023, apart from the continuing kokanee fishery in Lake Sutherland. A limited ceremonial and subsistence season for coho followed in autumn 2023. Reduced harvest was therefore another part of the recovery conditions measured by the researchers.

The first decade established several physical facts. Chinook and steelhead entered habitat above both former dam sites, redds spread through the middle and upper watershed, more adult Chinook remained in the river, and natural-origin juvenile Chinook production rose sharply after the worst sediment years passed.

It did not establish that the Elwha held a recovered wild Chinook population. Hatchery production still dominated adult returns, managers had relocated some fish upstream, and natural reproduction remained below replacement. Similar first-season caution is needed when reading early results from the Klamath River dam removals or longer recoveries such as the Kennebec River after Edwards Dam.

The Elwha is open now, but its Chinook run is still being remade one generation at a time. Each autumn, fish move through the channel where Lake Aldwell and Lake Mills once covered gravel, and the current passes the empty places where two walls stood.