WASCO, Ore. — For decades, most of the nation’s renewable power has come from dams, which supplied cheap electricity without requiring fossil fuels. But the federal agencies running the dams often compiled woeful track records on other environmental issues. Now, with the focus in Washington on clean power, some dam agencies are starting to go green, embracing wind power and energy conservation. The most aggressive is the Bonneville Power Administration, whose power lines carry much of the electricity in the Pacific Northwest. The agency also provides a third of the region’s power supply, drawn mostly from generators inside big dams. The amount of wind power on the Bonneville transmission system quadrupled in the last three years and is expected to double again in another two. The turbines are making an electricity system with low carbon emissions even greener - already, in Seattle, more than 90 percent of the power comes from renewable sources. Yet the shift of emphasis at the dam agencies is proving far from simple. It could end up pitting one environmental goal against another, a tension that is emerging in renewable-power projects across the country. Environmental groups contend that the Bonneville Power Administration’s […]