, the river forms the boundary between Lane County on the left and Linn County on the right. Curtis Slough enters from the right about from the mouth, where the river passes under bridges carrying the Southern Pacific and BNSF railways. The Willamette passes under U.S. Route 99E at RM 161 (RK 259) at Harrisburg, which is on the right. A United States Geological Survey (USGS) stream gauge, is on the right just beyond the highway bridge. Downstream of RM 160 (RK 260), the Willamette stops being the border between Lane and Linn counties, flows for about entirely in Linn County, then becomes the border between Linn County on the right and Benton County on the left. McCartney County Park straddles the river about from the mouth, and Ingram Slough enters from the left at the northern end of Ingram Island, about further downstream. Below this confluence, Anderson County Park is on the left. As the river curves around Irish Bend, Irish Bend County Park is on the left, and then Long Tom River enters from the left at Norwood Island, near RM 149 (RK 240). Meandering around Sam Daws Bend, the river splits to go around Hoacum Island. The main channel, rounding Snag Boat Bend, is re-joined by the side channel and arrives at Peoria, which is on the right. At this location, Peoria County Park is on the right. Below Peoria, the river subdivides at about from the mouth to form a complex set of linked sloughs and channels that flow around islands—McBee, Baker, Bear, John Smith, Centennial, Horseshoe, Kiger, Stahlbusch, and Fischer—before re-joining about downstream near Corvallis. In this stretch, the east channel of the river receives Muddy Creek from the right, and the main channel flows by Willamette Park and the Crystal Lake Sports Fields and Kendall Natural Area, all in Corvallis, on the river's left. Marys River enters from the left at about RM 132 (RK 212), at the Pioneer Boat Basin City Park. In Corvallis, the river passes under the Corvallis Bypass Bridge, which carries Oregon Route 34 Bypass, then flows by Kermit E. Ross City Park on the left and Alan B. Berg City Park on the right. It passes under the Van Buren Street Bridge, which carries eastbound Oregon Route 34 traffic, and then under the Harrison Street Bridge, which carries the highway's westbound traffic. U.S. Highway 20 runs roughly parallel to