Beginning in Upper St. Croix Lake in Douglas County, Wisconsin, the St. Croix River flows 164 miles to its confluence with the Mississippi River near Prescott, Wisconsin. The majority of the river creates the state boundary between Minnesota and Wisconsin. The upper St. Croix River flows past heavily wooded banks and islands. The upper 200 miles of the river is federally designated as a Wild and Scenic River. The lower St. Croix River showcases steep sandstone and limestone bluffs with winding side channels. This segment is also federally designated as a wild and scenic river.