Minnesota geography is dominated by three major watersheds which carry the surface waters of the state north to Hudson Bay, east to the Great Lakes, and south into the Mississippi River. The rivers, creeks, and associated lakes within these drainage basins essentially describe the route geography of the thoroughfares used by American Indians for centuries, and later by European explorers, missionaries, and fur traders. But water travel was subject to interruption caused by rapids, falls, or shallows, and not all of the major lakes and rivers were interconnected, making it necessary to portage from time to time.