the part of the Rhine River between the confluence of the Vorder- and Hinterrhein and its entry into Lake Constance. It is 63 miles (102 km) long. From Reichenau to Sargans it flows entirely within Swiss territory; for the next 19 miles (30 km) it forms the border between Switzerland and Liechtenstein; and the last part separates Switzerland from Austria. The river's waters are thick with mud.