Today, on a remote stretch of the Elwha River in northwestern Washington state, a demolition crew hired by the National Park Service plans to detonate a battery of explosives within the remaining section of the Glines Canyon Dam. If all goes well, the blasts will destroy the last 30 feet of the 210-foot-high dam and will signal the culmination of the largest dam-removal project in the world.

In Asia, Africa, and South America, large hydroelectric dams are still being built, as they once were in the United States, to power economic development, with the added argument now that the electricity they provide is free of greenhouse gas emissions. But while the U.S. still benefits from the large dams it built in the 20th century, there's a growing recognition that in some cases, at least, dambuilding went too far—and the Elwha River is a symbol of that.

The removal of the Glines Canyon Dam and the Elwha Dam, a smaller downstream dam, began in late 2011. Three years later, salmon are migrating past the former dam sites, trees and shrubs are sprouting in the drained reservoir beds, and sediment once trapped behind the dams is rebuilding beaches at the Elwha's outlet to the sea. For many, the recovery is the realization of what once seemed a far-fetched fantasy.

"Thirty years ago, when I was in law school in the Pacific Northwest, removing the dams from the Elwha River was seen as a crazy, wild-eyed idea," says Bob Irvin, president and CEO of the conservation group American Rivers. "Now dam removal is an accepted way to restore a river. It's become a mainstream idea."

Before the Park There Was the River

The Elwha runs for 45 miles, from the Olympic Mountains to the Strait of Juan de Fuca, and all but its final five miles lies within what is now Olympic National Park. Long before the park was established in 1938, the river was regionally famous as the richest salmon river on the Olympic Peninsula. For generations, the Lower Elwha Klallam Tribe, whose members live at the mouth of the Elwha, depended on the river's fish and shellfish for survival. But the peninsula was also famous for its massive trees, and in the early 1900s, the local timber industry needed power for its mills and its growing ranks of workers.

Fish were no match for finance, and the 108-foot-high Elwha Dam, located five miles upstream from the river's outlet, started generating power in 1914. "There is no question but that the Elwha is harnessed at last and forever," a local newspaper reporter crowed at the time. The larger Glines Canyon Dam, eight miles further upstream and inside what is now Olympic National Park, began operations in 1927.

View Images NG MAPS. SOURCES: Washington State Department of Ecology; Washington State Department of Natural Resources

For almost half a century, the two dams were widely applauded for powering the growth of the peninsula and its primary industry. But the dams blocked salmon migration up the Elwha, devastating its fish and shellfish—and the livelihood of the Lower Elwha Klallam tribe. As the tribe slowly gained political power—it won federal recognition in 1968—it and other tribes began to protest the loss of the fishing rights promised to them by federal treaty in the mid-1800s. In 1979, the U.S. Supreme Court ruled that Washington tribes, including the Elwha Klallam, were entitled to half the salmon catch in the state.

With this court victory behind them, the tribes began to fight for the protection and restoration of salmon runs. In the mid-1980s, the Elwha Klallam and environmental groups started to push for dam removal in earnest, arguing that their environmental costs and safety risks outweighed their benefits—especially because the Olympic Peninsula had long since been connected to the regional power grid, and the dams now provided only a small fraction of the power used by its residents and mills. In 1992 Congress authorized federal purchase of the two dams on the Elwha from the timber companies that owned them and ordered a study of the idea of removing them.

A Slow Demolition

It would take nearly two decades more for dam demolition to begin—much longer than it took to build the dams in the first place. The timber industry and some local communities opposed the idea, and U.S. Senator Slade Gorton of Washington blocked federal funding until he was voted out of office in 2000.

Though a few smaller dams had been removed from U.S. rivers, no one one had attempted a dam removal as large as the one proposed for the Elwha. The unknowns were daunting: What would happen to the estimated 27 million cubic yards of sediment (21 million cubic meters)—enough to fill the Seahawks' CenturyLink Field nine times over—trapped behind the dams? How would salmon and other wildlife respond to a free-flowing river? How would tribal members and other nearby residents be affected?

In 2004, the tribe, the National Park Service, and the city of Port Angeles reached an agreement on dam removal. The dams would be taken down in several stages, allowing for a relatively gradual release of sediment. Two water-treatment facilities would be built to protect local water supplies, and the tribe would receive federal funds for a new, larger fish hatchery.

Finally, on September 15, 2011, a barge-mounted excavator began chipping concrete off the upstream face of Glines Canyon Dam. Removal of the Elwha Dam began later that week. At a ceremony by the river, former Senator Bill Bradley of New Jersey praised the demolition of the dams in terms that wouldn't have sounded out of place at their inauguration. "The reflection you see in Elwha is an image of what our country is capable of," he told the crowd.

Six months later, the Elwha Dam was gone, and the river flowed in its original channel for the first time in more than a century. Steelhead and coho salmon transplanted above the dam site spawned in the river's tributaries, and juvenile coho were spotted. In the summer of 2012, Chinook salmon began migrating up the river, and by the following fall, they too had spawned in tributaries and in the Elwha mainstem.

"We had heard there would be all these positive changes," says Robert Elofson, river restoration director for the Lower Elwha Klallam Tribe and an early advocate of dam removal. "But to actually watch it in action—well, it's very, very impressive."

View Images In the world's largest dam removal project, the Elwha River now flows past the old Glines Canyon Dam (at bottom) in Olympic National Park. Photograph by Elaine Thompson, Associated Press

The River Returns

Over the past three years, the sediment trapped behind the dams has washed downstream, rebuilding riverbanks and gravel bars and, in and around the river's mouth, creating some 70 acres of new beach and riverside estuary habitat for Dungeness crabs, sand lance, surf smelt, clams, and other species. On the ocean bottom just offshore, what used to be a kelp-covered expanse of cobbles is now blanketed with mud and sand, also good habitat for crabs and sand lance. "We're seeing all sorts of different creatures. It's fantastic," says U.S. Geological Survey researcher Jonathan Warrick. The Elwha Klallam tribe hopes that eventually, its members will once again be able to harvest shellfish near the mouth of the Elwha.

As salmon populations recover, researchers expect the whole food web—from invertebrates to birds to otters and bears—to benefit. Smithsonian research fellow Christopher Tonra, who is studying American dippers on the Elwha, says that almost as soon as salmon returned to the river, the birds began to follow the fish and to eat salmon eggs and fry. "To see these birds that had never been exposed to spawning salmon before immediately respond to the resource—that's been really exciting," he says. Analysis of nitrogen isotopes in dipper blood, feathers, and toenail clippings suggests that the birds are indeed benefiting from the nutrients salmon provide.

Other animals have been slower to adapt to the changes on the Elwha. The reservoirs behind the Elwha and Glines Canyon dams have been drained and revegetated, and the young trees and shrubs are attractive food for deer, elk and other species. But the area's Roosevelt elk, known to be creatures of habit, have yet to discover the tasty vegetation growing behind the Elwha dam site.

"The buffet table has been set, and the elk are sometimes just a couple of hundred yards away," says Elwha Klallam tribe wildlife biologist Kim Sager-Fradkin. "But the elk haven't crossed the highway and discovered that the reservoir is gone. Once they find out, I don't know if they're ever going to leave."

The Elwha's recovery is not without controversy. The tribal fish hatchery has been criticized by some environmental groups for initially stocking a population of steelhead trout that's not native to the river. And though the river and its denizens appear to be thriving, both the dams and their removal have wrought great and lasting changes that won't readily be undone.

Rebecca Brown, a professor at Eastern Washington University who is studying the effects of the dam removal on riverside vegetation, says that the release of so much sediment in such a short time has created an ecosystem that's distinctive and likely to stay that way. "A thousand years from now, we're still going to be able to see the effects of this sediment dump," she says.

Dam Bust, Dam Boom

American Rivers reports that in the United States, nearly 850 dams have been removed in the last 20 years, with more than a hundred removed in 2012 and 2013 alone. "We're at the end of the large dam-building era in this country and the beginning of the river restoration era," says Irvin.

The Glines Canyon Dam, however, is the largest dam to be demolished so far and will likely remain so for some time. The Elwha's location in a national park fueled unusually broad support—and federal funding—for its restoration and simplified the logistics of dam removal. With climate change rendering much of the American West increasingly vulnerable to drought, the region cannot easily give up large dams that provide not only electricity but also water storage.

Meanwhile, hundreds of large dams are planned or under construction in developing countries. Demand for electrical power in urban Thailand, for example, is driving the construction of two large dams on the mainstem of the Mekong River, and nine more large dams are proposed—a cascade that threatens the productivity of the largest freshwater fishery in the world. A recent op-ed in the New York Times calls such large dams "brute-force, Industrial Age artifacts," arguing that they not only are environmentally and socially costly but also place huge financial burdens on the countries that build them.

Once the final section of the Glines Canyon Dam is removed this week, the remaining sediment behind it will begin to move downstream. Because of several years of low precipitation in the Pacific Northwest, sediment has so far moved more slowly than expected, and researchers hope a hearty flood or two will help move the rest. No matter the weather, however, the demolition means that salmon will regain access to the 75 miles of river habitat blocked by the dams.

Brian Winter, who has worked on Elwha River restoration for the National Park Service since 1993, is looking forward to seeing Chinook salmon swimming above the dam site, within the park's designated wilderness. The season's Chinook run has already started, so chances are slim that any fish will make it that far this year. But whether they return this year or next, he plans to hike in and see them arrive.

"I'll be there," he says. "I just want to sit on the bank and watch that happen."

Correction: An earlier version of this story used an incorrect name for Jonathan Warrick and mischaracterized the steelhead trout from the tribal fish hatchery.