The Bristol Bay region of southwest Alaska is home to the last great wild Sockeye salmon fishery in the world. It's also home to enormous mineral deposits - copper, gold, molybdenum - estimated to be worth some $300 billion. Now, two foreign mining companies are proposing to extract this mineral wealth by digging one of North America's largest open-pit mines, the Pebble Mine, at the headwaters of Bristol Bay. FRONTLINE travels to Alaska to probe the fault lines of a growing battle between those who depend on this extraordinary fishery for a living, the mining companies who are pushing for Pebble, and the political framework that will ultimately decide the outcome.