Somass River is a river on Vancouver Island, in the Canadian province of British Columbia. Its drainage basin is 1,412 square kilometres (545 sq mi) in size.
The river's name comes from a Nuu-chah-nulth word meaning "washing".
The Stamp River and Sproat River join to form the Somass River, which flows generally southeast and south into Alberni Inlet. The river crosses Highway 4 outside of Port Alberni.
Coordinates: 49°14′N 124°49′W / 49.233°N 124.817°W