This story is part of a special National Geographic News series on global water issues.

In Washington State's Olympic Peninsula, members of the Lower Elwha Klallam Tribe still tell stories of a time when the Elwha River was so full of salmon that a person could cross from one bank to the other by walking atop the thrashing bodies of fish struggling to move upstream.

No one has attempted such a feat since two dams were built, near the mouth of the river, in the early 20th century, blocking salmon runs.

But on September 15, officials in Olympic National Park will begin the long process of dismantling the Elwha and Glines Canyon dams on the Elwha River. (See a map of the region.)

The largest dam-removal undertaking in U.S. history, the project could serve as an inspiration and a model for similar enterprises in other parts of the country, conservationists say.

"Close to a thousand dams have been removed across our country, but these are the biggest," said Amy Kober, a spokesperson for the environmental group American Rivers.

"It is one of the most significant restoration efforts we have ever seen."

Dams No Longer Needed on Elwha

Completed in 1913, the 108-foot (33-meter) high Elwha Dam is situated about 4 miles (6.43 kilometers) from the mouth of the Elwha River. About 10 miles (16 kilometers) farther upriver sits the 210-foot-high (64-meter-high) Glines Canyon Dam, which was completed in 1927. (See more dam pictures.)

Both dams, constructed to provide electricity for a paper mill in the city of Port Angeles, were built without fish ladders, which allow salmon to navigate through dams.

The dams played an important role in the early development of the Olympic Peninsula at the turn of the last century but today are obsolete, because most of the region's power is now imported via an electric grid from Portland, Oregon.

The dams' removal had been proposed as far back as the 1970s, but was resisted by many of the local communities. Finally, a U.S. congressional act passed in 1992 paved the way for the U.S. government to acquire the dams and remove them in order to restore the river's ecosystem.

According to Kober, much of the initial resistance to the dams' removal was due to a fear of change. For many of the residents of Olympic Peninsula, the artificial lakes created by the dams' reservoirs were a natural part of the landscape, and their disappearance would be jarring. No homes or buildings would be threatened by the restored flow of the river.

But "over the years, people came to realize that the benefits of removing the dams far outweighed any benefits of keeping them," Kober said.

Despite the government’s support, nearly another decade would pass before the dams' deconstruction could begin. The barrier this time was cost, according to David Graves, Northwest program manager for the Washington, D.C.-based National Parks Conservation Association (NPCA).

"The final cost was estimated to be 351 million dollars, and it took many years to get that money together," he said.

Also, the 1992 act called for 43 projects to be completed before the dam dismantling process could start. These projects were designed to prepare the river and the region for the effects of the dams' removal.

For example, new water-treatment plants had to be constructed to deal with the predicted rise in river sediments, and levies had to be improved to protect private property along certain sections of the river where the water level was expected to rise.

Those safeguards now in place, engineers can finally begin slowly removing sections of the dams next month in a process that is expected to take about three years. The draining of the dams' reservoirs began earlier this summer.

The lumber mill that relies on the dam for power will begin looking for ways to generate power on site, Kober said.

Dam Removal Will Restore "Web of Life"

The razing of the dams will allow the Elwha's waters to once again flow free, and experts predict that the river's salmon populations will swell from their current number of about 3,000 to nearly 400,000.

The salmon—which include pink, chinook, coho, chum, sockeye, and other species—will once more have access to the more than 70 miles (113 kilometers) of waterways that make up the Elwha River and its tributaries. Currently, the fish can swim only a few miles upriver before the Elwha Dam blocks their passage.

Biologists say the return of the fish will benefit more than 130 species of plants and animals that have been deprived of a vital food and nutrient source for nearly a century.

"Everything from black bears to tiny insects and even orca whales will benefit. The salmon even fertilize the cedar trees along the river" after they die, Kober said.

"We're not just restoring the salmon—we're knitting back together the web of life, from the salt water of Puget Sound all the way up to the Olympic Mountains. There are going to be chain reactions throughout the whole ecosystem once the salmon start coming back."

Already changes to the river are apparent with the draining of the reservoirs, Kober noted.

"It's really starting to come back to life," she said. "We're already seeing it reclaim its old channels and its old shapes. ... As the water starts flowing again, we'll see new rapids being revealed."

Once the dams are gone, tons of trapped sediment and driftwood will also be free to flow downstream again.

"When a river is operating normally, sediment is washed downstream and out to sea, providing material for the shoreline," NPCA's Graves said.

"But for the past hundred years, all that sediment has been locked up behind the dams."

The discharged sediment could also benefit humans by forming a natural barrier against ocean waves at the mouth of the Elwha.

"Surfers are excited about how the new sand will improve the surf break near the river's mouth," American Rivers' Kober said.

Dam Removal May Inspire More Restoration

The lessons learned during the Elwha dams' removal will be valuable for future dam-removal projects, said NPCA's Graves.

"Scientists can look to these dam removals and see how easy or how hard it is to restore a river," Graves said.

"They can look at this and see what sort of projects need to happen beforehand, and once the dams are down how many years it takes for a river to return to its historic state."

American Rivers' Kober predicts the Elwha dams' removal will also inspire other restoration projects across the country.

"People are going to look at the Elwha and see it returning to health, and they're going to start asking questions about their own rivers," she said.

Salmon to Easily Return to River?

Biologists do not think the salmon will have any problems recolonizing their ancestral breeding grounds.

"They're programmed to do this," said Michael McHenry, a fisheries biologist for the Lower Elwha Klallam Tribe.

"Salmon have dealt with large scale disturbances across the Pacific Northwest landscape for millions of years. They've dealt with glaciation, volcanic eruptions, and huge landslides that probably temporarily eliminated them from parts of their range."

In comparison, the dams, which have been around for only a century, are "a blink in geologic time," McHenry said, and should not pose any major challenges for the returning salmon.

But whether the fish will return in strong enough numbers to allow for salmon walks across the river once again remains to be seen, especially with other pressures on the fish, such as overfishing.