In this Sept. 4, 2011, file photo, smoke rises from the stacks of the main plant facility at the Navajo Generating Station, as seen from Lake Powell in Page, Ariz. Two companies that sought to take over the coal-fired power plant on the Arizona-Utah border have ended efforts to acquire it. New York-based Avenue Capital and Chicago-based Middle River Power showed interest but said Thursday, Sept. 20, 2018, they could not overcome the challenges. (Ross D. Franklin/AP, File)