The Coos River flows for about into Coos Bay along the Pacific coast of southwest Oregon in the United States. Formed by the confluence of its major tributaries, the South Fork Coos River and the Millicoma River, it drains an important timber-producing region of the Southern Oregon Coast Range. The course of the main stem and the major tributaries is generally westward from the coastal forests to the eastern end of Coos Bay near the city of Coos Bay. The river is the largest tributary of Coos Bay, which at about is the largest estuary that lies entirely within Oregon. The river enters the bay about from where the bay—curving east, north, and west of the cities of Coos Bay and North Bend and passing by the communities of Barview and Charleston—meets the ocean. About 30 other tributaries also enter the bay directly. Most of the Coos River watershed of is in Coos County, but are in eastern Douglas County. Commercial forests cover about 85 percent of the basin. The river supports populations of chinook and coho salmon, shad, steelhead, and coastal cutthroat trout. Since public river-bank access is limited, fishing is often done by boat.
Course
Flowing west from the confluence of the South Fork Coos River and the Millicoma River, the Coos River is bordered by Oregon Route 241 on the and Coos River Road on the. Downstream from its source, the river receives Noah Creek from the right from the river mouth. Curving south, the river receives Vogel Creek and then Lillian Creek, both from the left, before passing under Chandler Bridge, which carries Route 241 from the right bank to the left bank about from the mouth. The river then turns west and north as it enters the bay and splits into two distributaries separated by a marsh. The Cooston Channel, which is on the right, continues north around the west side of the marsh for about to the mouth. The left-hand channel almost immediately merges with Catching Slough, which enters from the left and continues around the east side of the marsh to meet the Marshfield Channel of the bay.
Discharge
Estimates of the average discharge of the Coos River varies from in late summer to in February. Estimated extremes vary from a low of to a high of.
