A plan to tear down two dams on the north Olympic Peninsula -- one of which would be the tallest dam intentionally removed in U.S. history -- won the approval Wednesday of Washington environmental regulators.

Knocking down the Elwha and Glines Canyon dams on the Elwha River west of Port Angeles is expected to indirectly benefit Puget Sound's orcas. That's because it would open up about 70 miles of spawning grounds for chinook salmon, the orcas' main food source.

Prolific salmon runs came out of the Elwha before the dams were built early in the last century to generate power. By some estimates, restoration of the Elwha represents the largest single opportunity to boost chinook runs formerly used by the orcas.

The state Ecology Department, as expected, issued an order Wednesday clearing the way for the removals, scheduled to start in 2009.

"It's a big milestone, a giant step in the right direction," said Amy Kober of the Seattle office of American Rivers, an environmental group that has pushed strongly for the project.

The larger of two dams, the Glines Canyon, is 210 feet tall. Since environmentalists generally began pushing for dam removal several decades ago, the largest dam removed has been the Occidental Chem Pond Dam D in Tennessee, Kober said. That dam, removed in 1995, was 160 feet tall.

The plan to remove the dams brought up a host of environmental issues. The most important was whether releasing about 18 million cubic yards of dirt and rock that have built up behind the dams would violate water quality standards.

Ecology found that while that would temporarily cloud water, the project would prove ecologically beneficial on balance -- and might even help reverse the erosion of such beaches in the area as Ediz Hook.

A 1996 federal study predicted that the removals would generate $164 million in tourism and sport-fishing benefits in the century after the dams are taken down.

The project requires additional permits, including one from the U.S. Army Corps of Engineers. However, the process has not been controversial because of negotiations overseen by U.S. Rep. Norm Dicks, D-Wash.

"The Elwha River once hosted a famous run of chinook salmon," Gov. Chris Gregoire said in a press release. "These fish were huge, some weighing over 100 pounds, and they have been all but eliminated by these two dams."