- The Wynoochee River is a 60-mile (97 km) long river located in the Olympic Peninsula in the U.S. state of Washington. A tributary of the Chehalis River, the Wynoochee River rises in the Olympic Mountains within the Olympic National Park and flows generally south. Its drainage basin is 218 square miles (560 km2) in area. The name Wynoochee comes from the Lower Chehalis placename /x??n�?c/, meaning “shifting”.