river rising in Lac Vieux Desert (lake), Vilas county, northern Wisconsin, U.S., on the Wisconsin-Michigan border. It flows generally southward through central Wisconsin past Rhinelander, Wausau, Stevens Point, Wisconsin Rapids, and Wisconsin Dells (site of a scenic gorge). The river then turns southeast to just past Portage and then southwest and west to join the Mississippi River near Prairie du Chien after a course of 430 miles (690 km). It has a drainage basin of some 12,000 square miles (31,000 square km).

In 1673 the French explorers Jacques Marquette (Marquette, Jacques) and Louis Jolliet (Jolliet, Louis) traveled down the Wisconsin River from Portage to the Mississippi. The Wisconsin is navigable for light craft as far as Portage, 200 miles (320 km) from its mouth, but navigation farther upstream is made difficult by shifting sandbars. At Portage the Fox River (connected to the Wisconsin by a canal that has been in disuse for navigation since the mid-20th century) is only 1.5 miles (2.5 km) by land to the northeast across low, marshy ground. Several lakes were formed by dams, including Lake Wisconsin and Castle Rock and Petenwell lakes.