Can a river recover when you remove its dams? The Elwha story
Two dams blocked a Washington river's salmon for over a century. In 2011 what was then the largest dam removal in history began, and the river started to move its mud again.
▶ Start the storyYes, a river can start to recover when its dams come out, and the Elwha River in Washington State shows how. From 1911 to 2014, dams blocked fish passage on the lower Elwha. Before the dams, 400,000 adult salmon returned each year to in 70 miles of river. Before removal, fewer than 4,000 returned, in only 4.9 miles of habitat below the lower dam.
Adult salmon returning to the Elwha each year
adults
| Salmon returns | |
|---|---|
| Before the dams | 400,000 adults |
| Before removal | 4,000 adults |
The dams had a messy beginning. The builder of the Elwha Dam, Thomas Aldwell, cut corners, including illegally not building fish passages, and the dam's lower sections gave way in 1912 as the reservoir filled. The dams helped fuel local economic growth, but by the early 21st century their combined output equalled only 38 percent of the electricity needed to run one sawmill.
The damage went beyond blocking fish. After the dams were built, the lower river got far less , causing net erosion of the riverbed, including the gravels that fish need to . Warmed reservoirs also increased parasite populations that threatened salmon runs. Because the best spawning habitat lay far upstream, removing both dams was considered the only viable option.
In 1992 a law authorized the federal government to acquire the two dams for demolition and habitat restoration. Removal of the Elwha Dam began in September 2011 and was complete by March 2012. The 210-foot Glines Canyon Dam came out by 2014; as of 2025 it was still the tallest dam ever intentionally . By November 2014, 30 percent of the stored had reached the river's mouth, creating 70 acres of new habitat.
Recovery takes time. Fish may return as soon as a year after removal, but full return to pre-dam conditions may take 15 to 20 years.
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Recap
Take the wall down and the river moves its mud and fish again, but full recovery takes decades.
💡 A trick to remember it · Like a cast coming off a broken leg: the river can move again right away, but it takes years before it walks the way it used to.
Surprising fact · By November 2014, 30 percent of the stored sediment had reached the river's mouth and made 70 acres of new estuary.
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Sources (4)
No source, no claim. Every fact in this lesson (17 claims) cites at least one of these.