Rivière Moisie, 410 km long, rises in eastern Québec from Lac Opocopa and flows south to the St. Lawrence River. With a drainage basin of 19,200 km2 and a mean discharge of 490 m3/s, it is the river of greatest volume along the middle north Shore of the St. Lawrence. Its current is swift and its rapids are numerous. The deep, rugged valley is lined with spruce, fir, birch, aspen and pine. It is one of the best salmon and trout rivers in eastern North America. The HBC has a trading post at the village of Moisie at the river's mouth, some 20 km east of Sept-Îles. The name possibly derives from a Montagnais personal name.