Chehalis River (Washington) (Wikipedia) The Chehalis River (/ʃəˈheɪlɪs/ shə-HAY-lis) is a river in Washington in the United States. It originates in several forks in southwestern Washington, flows east, then north, then west, in a large curve, before emptying into Grays Harbor, an estuary of the Pacific Ocean. The river is the largest solely contained drainage basin in the state.