The Pacific Northwest's epic rivers are home to primordial runs of endangered wild salmon and to river-blocking dams that generate power. What happens when the dams get too old? The Marmot Dam outside of Portland, Ore., is almost 200 feet long and stands nearly five stories high. Built almost 100 years ago, it's too expensive to modernize and instead will be removed. It will take engineers, explosives experts, river scientists and weather forecasters to construct the best destruction plan.
