The Mistassibi River is a river in central Quebec, Canada. It is 298 kilometres (185 mi) long and has a drainage basin of 9,325 square kilometres (3,600 sq mi). Its source is an area with unnamed lakes about 50 kilometres (31 mi) east of Canso Bay of Lake Albanel, eastern neighbor of Lake Mistassini. The name Mistassibi, only in use since the late 19th century, comes from the Innu-aimun language, meaning "large river". Its alternate name used to be Rivière aux Foins (Hay River).