The Red River of the North starts at the confluence of the Bois de Sioux and Otter Tail rivers and forms most of the border between Minnesota and North Dakota. It then crosses into Manitoba and empties into Lake Winnipeg before its waters finally flow into the sea at Hudson Bay. Cities have grown up along its banks including Fargo, Grand Forks and Winnipeg and their residents are all too aware of one unfortunate feature of the river. Unlike most large U.S. rivers, it flows from south to north.