The Bonneville Power Administration and Army Corps of Engineers announced Thursday they intend cut off water spilled over Ice Harbor and John Day dams during the last five days of August, rather than their previous proposal to cut the spill for the last 10 days.

They left in place a plan to cut off summer spill for all of August at Bonneville and The Dalles dams.

With this change, dam managers estimate they will generate $18 million to $28 million in electricity sales in August, down from an anticipated $20 million to $31 million.

Spilling water provides a safer journey than shooting fish through turbines, where they may clang off turbine blades or suffer an effect similar to the bends in deep-sea divers. But it also saps the dams' ability to generate electricity, reducing Bonneville's ability to sell surplus power to California and the Southwest.

Bush administration officials acknowledge their plan will reduce the number of Columbia basin fall chinook by as many as 12,000 fish when they're ready to return to spawn in three to four years.

But they say a series of other measures, including $2 million for habitat restoration, should more than offset the fish killed in dam turbines. They noted that the spill reduction will affect only one endangered run of fish Snake River fall chinook and result in a reduction of only about a dozen of the 2,500 expected to return to spawn in three or four years.

"If we can run the system more efficiently, and save Northwest ratepayers $18 (million) to $21 million, the question would be: Why would you not do that?" BPA spokesman Mike Hansen said.

Northwest utilities have pressed Bonneville for cost reductions in recent years. BPA increased wholesale rates by 46 percent in the fall of 2001, on the heels of a drought and a West Coast energy crisis fueled by profiteering.

Conservation and tribal groups have vowed to sue over Bonneville's latest proposal, contending that spilling water for fish is no more wasteful than dedicating water for irrigation, navigation or flood control.

Bonneville officials say they expect their spill-reduction plan will shave 1 or 2 percentage points from its wholesale rates.

"What surprises me the most about this is how much they're willing to risk for so little in return," said Andrew Englander, a policy analyst for Save Our Wild Salmon in Portland. "The benefits to your average residential taxpayer is miniscule. We've got to believe there's a better way for this agency to reduce rates."