Fox, river, 176 mi (283 km) long, rising in S central Wis. and flowing SW to within 1.5 mi (2.4 km) of Portage, Wis., on the Wisconsin River, then NE through Lake Winnebago into Green Bay, an arm of Lake Michigan, at Green Bay, Wis.; the Wolf River is its main tributary. The cities of Appleton and Oshkosh are on the Fox. Rapids at points along the river furnish water power. The river was a well-known route used by early explorers, missionaries, and fur traders to reach the Northwest and the Mississippi River system from the Great Lakes. A barge canal links the Fox and Wisconsin rivers at Portage, forming a continuous waterway from Lake Michigan to the Mississippi River.