PORTLAND, Ore. – A long-awaited federal report out Friday rejected the idea of removing four hydroelectric dams on a major Pacific Northwest river in a last-ditch effort to save more than a dozen species of threatened or endangered salmon, saying such a dramatic approach would destabilize the power grid, increase overall greenhouse emissions and more than double the risk of regional power outages. The four dams on the lower Snake River in eastern Washington are part of a vast and complex hydroelectric power system operated by the federal government in Washington, Oregon, Idaho and Montana. Environmental groups who have pushed for years for the dams to come down immediately blasted the report.