Yellowstone National Park is in trouble. This national treasure, a once pristine and virtually untouched ecosystem, is under attack from a merciless invader that has the power to change America's first national park forever. This attack is not from man or machine...the intruder with the power to alter one of the most iconic natural preserves in the world is...a fish. Lake Trout were first discovered in Yellowstone Lake nearly 30 years ago. No one knows exactly how they got there but this very effective predator prospered by feeding on the world's only existing population of native Yellowstone Cutthroat trout. Now, the native cutthroat population has been decimated and the effects of the loss of this one species is having serious negative and irreversible effects across the landscape.