On Wednesday, workers will breach the last dams in a key stretch of the Klamath River, allowing salmon to swim unhindered through a vital watershed near the California-Oregon border for the first time in more than a century. The largest dam-removal project in U.S. history is nearing completion.

Crews used excavators to remove rock dams that diverted water upstream from two dams, Iron Gate and Copco No. 1, both of which were already almost completely removed. Each shovelful allowed more and more river water to flow through the historic channel. The work, expected to be completed by this evening, will provide salmon with passage to important habitat in time for the Chinook salmon spawning season in the fall.

“Our sacred duty to our children, our ancestors and ourselves is to take care of the river, and today’s events represent a fulfillment of that obligation,” Frankie Myers, vice chairman of the Yurok Tribe, which has fought for decades to remove the dams and restore the river, said in a statement.

The demolition came about a month before the demolition of four massive dams on the Klamath was scheduled to be completed. The demolition was part of a nationwide movement to return rivers to their natural flow and restore ecosystems for fish and other wildlife.

As of February, more than 2,000 dams had been removed in the U.S., most in the past 25 years, according to the advocacy group American Rivers. Among them were dams on Washington state’s Elwha River, which flows from Olympic National Park into the Strait of Juan de Fuca, and the Condit Dam on the White Salmon River, a tributary of the Columbia.

“I am excited to begin the restoration phase of the Klamath River,” Karuk Tribal Chairman Russell “Buster” Attebery said in a statement. “Restoring hundreds of miles of spawning grounds and improving water quality will help support the return of our salmon, a healthy, sustainable food source for multiple tribal nations.”

Salmon have cultural and spiritual significance to the tribe and other tribes in the region.

The Klamath was once the third-largest salmon river on the West Coast. But after energy company PacifiCorp built the dams to generate electricity between 1918 and 1962, the structures disrupted the river’s natural flow and interrupted the life cycle of the region’s salmon, which spend most of their lives in the Pacific Ocean but return to their home rivers to spawn.

Fish populations then declined dramatically. In 2002, a bacterial outbreak caused by low water levels and high temperatures killed more than 34,000 fish, mostly Chinook salmon. This was the beginning of a decades-long effort by tribes and environmental groups that culminated in 2022 when federal authorities approved a plan to demolish the dams.

Meanwhile, the smallest of the four dams, Copco No. 2, has been removed. Workers have also emptied the water reservoirs of the other three dams and began demolishing these structures in March.

Along the Klamath, the dams will not have a major impact on power supplies. At full capacity, they produced less than 2% of PacifiCorp’s energy – enough to power about 70,000 homes. Hydropower from dams is considered a clean, renewable energy source, but many larger dams in the Western U.S. have become targets of environmental groups and tribes because of the damage they cause to fish and river ecosystems.

The estimated cost of the project was approximately $500 million, which would be paid for by taxpayers and PacifiCorps taxpayers.

Oregon Republican Senator Dennis Linthicum opposed the dam demolition, arguing that the project would destroy important sites for water storage, flood control and fire prevention.

“We have fisheries and hatcheries that have been there for years, and salmon have been catching there for years, but somehow that’s ‘not good enough,'” he said. “To make history, the salmon have to swim further up, over the dam, past JC Boyle,” referring to a dam upstream.

It is unclear how quickly salmon will return to their original habitats and the river will recover. There are already reports of salmon at the river mouth beginning their journey. Michael Belchik, senior water policy analyst for the Yurok Tribe, expressed hope that they will pass the Iron Gate Dam soon.

“I think we’re going to have some initial success,” he said. “I’m pretty confident we’re going to see some fish swim over the dam. If not this year, then certainly next year.”

There are two more Klamath dams further upstream, but these are smaller and allow salmon to pass over fish ladders – a series of pools through which fish can jump to get past a dam.

Mark Bransom, executive director of the Klamath River Renewal Corporation, a nonprofit organization that oversees the project, pointed out that it took about a decade for the Lower Elwha Klallam Tribe to start fishing again after the Elwha dams were demolished.

“I don’t know if anyone knows for sure what this means for the fish to return,” he said. “It’s going to take some time. You can’t undo 100 years of damage and impacts to a river system overnight.”