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 up to $500 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.