The greater prairie chicken, an endangered species in some states, was once a classic rural icon, but now its future is less certain. In northwestern Minnesota, there was once a huge glacial lake, Lake Agassiz, that formed after the last ice age. It covered an area that stretched from Canada on its northern border to South Dakota at its southernmost point. Today, all that is left of the ancient lake are the defined beach ridges and the Red River of the North that flows into Canada.