river in western Quebec province, Canada. The river drains Lake Matagami at 765 feet (233 m) above sea level, flows northwestward for 140 miles (225 km), and empties into Rupert Bay at the south end of James Bay. Its chief headstreams, the Bell, Chibougamau, and Waswanipi, all flow into Lake Matagami; each adds more than 150 miles (240 km) to the length of the main stream. The swift-flowing Nottaway, with its great hydroelectric potential, was explored by Robert Bell, a Canadian government geologist, in the 1870s.