The Bush administration yesterday asked a federal appeals court convened in Seattle to end the forced spilling of water over four Snake and Columbia river dams, saying the effort already has harmed some of the salmon that were supposed to be helped.

"It is quite extraordinary," said Justice Department attorney Ellen Durkee. "This is an untested experiment on a listed species with unknown consequences."

Environmentalists and other backers of the spill disputed that assessment, and urged the three-judge panel of the 9th Circuit Court of Appeals to let stand a U.S. District Court judge's order as a way to ease the downriver passage of young Snake River fall chinook.

"The spill is working," said Todd True, an attorney for Earthjustice Legal Defense Fund. "Juvenile salmon are getting down the river. Adult salmon are getting up the river. This is not a grand experiment."

The hearing was just the latest clash in a lengthy battle over management of the Columbia River basin hydropower system, which is a major obstacle to salmon migration.

The appeals court did not indicate when it would rule.

Federal fisheries officials have backed the use of barges to carry young salmon around Lower Granite, Little Goose and Lower Monumental dams on the Snake River, and McNary Dam on the Columbia River. They say that's the best route for salmon that also allows the Army Corps of Engineers to flow most of the water through turbines to generate hydropower.

But in May, U.S. District Judge James Redden of Portland threw out a Bush administration plan for protecting salmon in the rivers, saying it didn't sufficiently consider the harmful effects of the dams. Redden ordered federal dam managers to spill most of the water over the dams in an effort to help downstream migration.

The Bonneville Power Administration initially estimated that the spillage could cost $67 million in lost revenue.

While the two sides battle in court, federal officials say that the spill now is going relatively well.

• When the spill first began June 20, falling water at Little Goose Dam created a whirlpool that appeared to block adult salmon from finding a fish ladder. Upstream migration rates plummeted until the spill was reduced. But the delay in upstream migration may have weakened some of the fish, said Bob Lohn of National Oceanic and Atmospheric Administration Fisheries.

• During four days in June, the spill increased levels of dissolved gases below Little Goose Dam. The higher levels violated state standards and could have harmed migrating fish if they didn't move to deeper, safer water, according to some federal fishery biologists.

Even so, environmentalists said that those early problems with the spill were minimal and have been outweighed by the benefits to young salmon moving downriver.

"There had to be a few tweaks, and we worked with them to do that," True said.

Hal Bernton: 206-464-2581 or hbernton@seattletimes.com

The Associated Press

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