A federal judge ordered U.S. officials to increase the volume of water spilled through five dams on the Snake and Columbia rivers to make it easier for imperiled salmon species to reach the ocean.

U.S. District Judge James Redden, however, rejected a request to increase by 10 percent the speed of the rivers' water flow. Environmentalists had said that would lower water temperatures and further help the salmon migrate to the sea.

"The fall chinook run is in danger" because of the small amount of water spills, Redden said at a hearing Friday. "The law says you can't do that."

Government agencies named in a lawsuit over the protection of the salmon -- including the Bonneville Power Administration, the National Oceanic and Atmospheric Administration's Fisheries Service and the U.S. Army Corps of Engineers -- said in a joint statement that they may appeal the ruling to the U.S. Court of Appeals for the 9th Circuit.

"We are extremely concerned that the outcome provides no guarantee for the improvement of salmon stocks and it could make things worse at an enormous cost to the region," the statement said.

Redden's ruling in favor of environmentalists, American Indian tribes and people who fish calls for increases in water passing through spillways in four dams on the Snake River and in the McNary Dam on the Columbia.

Environmentalists say the spills will allow the 12 threatened and endangered salmon species to more safely pass through the dams on their way to the sea and, upon returning, to spawn than when they pass through the turbines on the dams. The turbines generate electricity for the Pacific Northwest, but they also kill many of the salmon.

The Bonneville Power Administration estimated that the extra spill will cost about $67 million, about a 2 percent increase in rates for residential customers. The first spills are scheduled to begin in less than two weeks.

Friday's ruling "said the federal government cannot walk away from its responsibilities for salmon and to the communities that rely on them," said Jan Hasselman of Seattle, an attorney with the National Wildlife Federation, the lead plaintiff in the case.

Last month, Redden struck down the Bush administration's $6 billion plan for salmon recovery, saying it fell short of protecting the imperiled fish.

Fishermen, environmentalists and Native American tribes say the McNary Dam on the Columbia River is one of the dams that inhibit salmon runs.