When John Charles Fremont visited Dakota Territory in 1839, he encountered a large body of water and attempted to describe what he saw. “Enchanting Water,” he penned in his journal, “is a beautiful sheet of water, the shores being broken into pleasing irregularity by promontories and many islands.” He noted the water was “brackish” but that it was “doubtless freshened by the rains and melting snow of the spring.” What’s more, it had fish. As enc…