river, the main channel flows north by Sauvie Island, which is on the left and marine terminals and industrial areas, which are on the right. About from the mouth, the Columbia Slough enters from the right. Kelley Point Park is to the right at the confluence of the Willamette and the Columbia, about from the larger river's mouth on the Pacific Ocean. The elevation at the mouth is about above sea level. The reaches of the river below Willamette Falls are influenced by tidal effects from the Columbia River. Over its entire course, the main stem of the Willamette varies from about in width. Multnomah Channel The Willamette's smaller distributary, the Multnomah Channel, flows northwest then north around Sauvie Island for about to meet the Columbia River near the city of St. Helens, in Columbia County. U.S. Route 30 and tracks of the Burlington Northern Railroad run roughly parallel to the channel, and to its left, between its source and the Multnomah–Columbia county border at about RM 12.5 (RK 20.1). In its first , the channel receives Miller Creek from the left, then passes under Sauvie Island Bridge, which carries Northwest Sauvie Island Road. Below the bridge, Ennis Creek enters from the left, then McCarthy Creek from the left at RM 18. Further along, Johns Creek enters from the left, and then Joy Creek enters from the left where the channel leaves Multnomah County and enters Columbia County. About from the mouth, the channel flows around Coon Island. Shortly thereafter, Crane Slough, which drains Crane's Lake, and the Gilbert River, which drains Sturgeon Lake, enter from the right. Then the channel receives Jackson Creek from the left and Cunningham Slough from the right before flowing around Louse Island and merging with Scappoose Bay, which is on the left. St. Helens is on the left as the channel enters the Columbia, about from the larger stream's mouth on the Pacific Ocean. Discharge Ranking 19th in volume among U.S. rivers, the Willamette makes up 12 to 15 percent of the total flow of the Columbia River. The flow at the Willamette's mouth averages about , although it varies from about in August during the dry season to more than in December. The United States Geological Survey (USGS) operates four stream gauges along the river, at Harrisburg, Albany, Salem, and Portland. The oldest of these, at Albany, has collected discharge data since the