WASHINGTON — The Obama administration and California officials are expected to announce a landmark agreement Wednesday to tear down four hydroelectric dams on the Klamath River, bypassing Congress to restore a major salmon fishery on the Oregon border.

The dam removals would set in motion the largest river restoration in U.S. history and signal an end to one of the most contentious water fights in years. Since 2001, the Klamath basin has seen farmer bucket brigades, clashes with American Indian tribes, commercial fishery shutdowns and the largest fish die-off ever on the West Coast.

A high-profile news conference to announce the deal is set for Wednesday at the Yurok Reservation in Klamath (Del Norte County), with Gov. Jerry Brown joining Oregon Gov. Kate Brown; Interior Secretary Sally Jewell; National Oceanic and Atmospheric Agency Administrator Kathryn Sullivan; and Stefan Bird, chief executive of Pacific Power, a division of PacifiCorp, which owns the dams.

States work with feds

“The two states and Secretary Jewell decided this is too important a place to too many people to walk away from trying to solve these tough problems,” said California Fish and Wildlife Director Chuck Bonham.

“We more or less locked ourselves up and we produced the details” of the dam removal after outlining the deal two months ago, Bonham said.

State officials decided to move forward on a 2010 pact among the warring Klamath basin parties. That pact called for dismantling the dams but required congressional approval. Republicans, especially Californians opposed to dam removals in general, refused to consider legislation and let the pact expire in December.

The parties now intend to bypass Congress by using a dam delicensing process at the Federal Energy Regulatory Commission, an agency that oversees hydroelectric power. The plan calls for removing the four dams by 2020, the same timeline set by the original pact.

“What we believe we’ve found here is a way to go forward that doesn’t require approval from Congress,” said Bob Gravely, spokesman for PacifiCorp.

The company will pay the first $200 million of the cost of removing the J.C. Boyle, Iron Gate, and Copco 1 and 2 dams. Estimates of the full job run as high as $450 million.

Brown has proposed setting aside $250 million to finish the job, which the Legislature would have to approve. No federal funds will be used.

Less cost, less risk

Keeping the dams could cost as much as removing them. They block about half the Klamath River basin, so relicensing them would require fish ladders and other major capital improvements. Costs for modernization are estimated at about $400 million.

“Having them removed and replacing the power will cost less and lead to less risk than proceeding with relicensing under known terms and conditions,” Gravely said.

The dams were commissioned in the 1940s and ’50s for hydroelectric power, not to store water or prevent floods. Two of the dams created large reservoirs, used for recreation and lined in some places with private homes.

Pacific Power’s 600,000 affected customers have been paying a dam removal surcharge of up to 2 percent of their electricity bills, Gravely said, with about half the cost, $100 million, now set aside.

Brian Johnson of Trout Unlimited, a sport fishing and environmental group involved in the negotiations, said that the dams have blocked half the watershed of the Klamath and that removing them will “open up close to 500 miles of steelhead habitat and about 420 miles for salmon.”

Dams disrupt river ecologies, blocking salmon migrations to upstream spawning habitat and preventing the deposition of sediment downstream that nurtures coastlines.

The Federal Energy Regulatory Commission also has to approve the delicensing plan in a public process at which opponents, mainly farming interests and dam removal opponents, are expected to object.

Rep. Jared Huffman, D-San Rafael, whose district includes some of the basin, said that the new deal will not include assurances of water to basin farmers, but that “I think (the farmers) are going to be fine.”

Bypasses Congress

“The essence of the deal is a private dam owner who wants to get rid of these zombie dams that don't provide a lot of hydropower and have huge environmental liabilities, and can be part of a transformative river restoration,” Huffman said. “None of this requires any approval or authority or appropriation from Congress.”

Carolyn Lochhead is The San Francisco Chronicle’s Washington correspondent. Email: clochhead@sfchronicle.com