The Willamette River is a tributary of the Columbia River in the U.S. state of Oregon. The upper tributaries of the Willamette originate in mountains south and southeast of the twin cities of Eugene and Springfield. Formed by the confluence of the Middle Fork Willamette River and Coast Fork Willamette River near Springfield, the main stem meanders generally north from source to mouth. The river's two most significant course deviations occur at Newberg, where the stream turns sharply east, and about downriver from Newberg, where it turns north again. Near its mouth, the river splits into two channels that flow around Sauvie Island. The main channel enters the Columbia about from the larger stream's mouth on the Pacific Ocean, and the smaller Multnomah Channel enters the Columbia about further downstream near St. Helens in Columbia County.
Incorporated Cities along the Willamette's course include [Springfield and Eugene in Lane County; Harrisburg in Linn County; Corvallis in Benton County; Albany in Linn and Benton counties; Independence in Polk County; Salem in Marion and Polk Counties; Keizer in Marion County; Newberg in Yamhill County; Oregon City, West Linn, Milwaukie, and Lake Oswego in Clackamas County (Small portions of the later two extend into Multnomah County), and Portland in Multnomah County. (Parts of Portland are also in Washington County, but the Willamette never makes contact with Washington County.) Significant tributaries include the McKenzie, Long Tom, Marys, Calapooia, Santiam, Luckiamute, Yamhill, Molalla, Tualatin, and Clackamas rivers.
Arising at above sea level, the river loses in elevation between source and mouth or about 2.3 feet per mile (43 cm per km). The gradient is slightly steeper from the source to Albany than from Albany to Oregon City. At Willamette Falls, the river plunges about . For the rest of its course, the river is extremely low-gradient and is influenced by Pacific Ocean tidal effects from the Columbia. The main stem of the Willamette varies in width from about .
Contributing forks
The Middle Fork and the North Fork—a tributary of the Middle Fork—rise on the western side of the Cascades between Three Sisters Wilderness on the north and Diamond Peak Wilderness on the south. Originating in Douglas County, the Middle Fork receives the North Fork northwest of Oakridge in Lane County and flows northwest through the mountains to the southern end of the Willamette Valley. The Coast Fork, draining part of the Calapooya Mountains south of Cottage Grove and part of the eastern slopes of the Oregon Coast Range, begins in Douglas County and flows north to join the Middle Fork about southeast of Eugene. The elevation at the source of the mainstem Willamette is above sea level. Source elevation derived from Google Earth search using GNIS source coordinates.Williams, pp. 27 and 32–33
Eugene–Springfield to Albany At the Willamette's source, the confluence of the two forks, Dorris Ranch Living History Farm is on the right and Franklin Boulevard is on the left. Interstate 5 (I-5), co-terminous with Oregon Route 99 (Pacific Highway), is also on the left bank slightly further from the river than Franklin Boulevard. For its first , the river flows north. It passes Willamette Heights Park, which is on the right, then enters the city of Springfield. The river then flows under a Southern Pacific Railroad bridge and under a bridge carrying Business Route 126 (Main Street); Millrace Park is on the upstream side of the second bridge, and Island Park is on the downstream side, both on the right. The unincorporated community of Glenwood is on the left.Williams, p. 51
Turning sharply west at river mile (RM) 185 or river kilometer (RK) 298, the river flows by West D Street Greenway in Springfield, which is on the right, before passing under I-5 and turning northwest and entering Eugene. On the river's right beyond I-5 is Alton Baker Park, and on the left is Route 99, coterminous with Business Route 126. Along this stretch, the Willamette flows under the Knickerbocker Bicycle Bridge, the Dave and Lynn Frohnmayer Pedestrian and Bicycle Bridge (formerly the Autzen Bicycle Bridge), and the Peter DeFazio Bridge before reaching the Ferry Street Bridge, which carries Coburg Road. The river then passes Skinner Butte Park, which is on the left, and under Interstate 105 (I-105). Turning north, the river flows between East Bank Park on the right and West Bank Park on the left and passes under the Greenway Bike Bridge and then the Owosso Bike Bridge before passing under Oregon Route 569 (Beltline Highway) and leaving the city. Just downstream of the highway, Dedrick Slough enters from the right and then Dodson Slough, also from the right, before the river flows around Confluence Island and receives the McKenzie River from the right north of Eugene and from the Willamette's mouth.
Meandering north, the river receives Spring Creek from the left about later, then flows around Marshall Island before reaching Linn County at about RM 167 (RK 269). For about the next , 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.Williams, p. 63
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.Williams, p. 81
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 the river on its left bank from Corvallis to Albany.Williams, p. 101
Below Corvallis, the Dead River enters from the right at Half Moon Bend, from the mouth. About downstream, a side channel called the Kiger Cutoff, in concert with the main channel, helps form Lower Kiger Island. Below the island, the river reaches Bowers Rock State Park at RM 123 (RK 198), where Bowers Slough enters from the left and the Little Willamette River enters from the right. On the opposite bank from the state park, the much smaller Hyak County Park is on the left. As the river reaches Albany, the Calapooia River enters from the right from the Willamette's mouth. Bryant Park is on the right, and a USGS stream gauge is just beyond the confluence, where the combined rivers flow under the Ellsworth Street Bridge and then the Lyon Street Bridge, which carry U.S. Route 20 eastbound and westbound, respectively. The gradient is slightly steeper in these upper reaches than in the reaches between Albany and Oregon City.
Albany to Oregon City
In Albany, the river flows east under a Union Pacific railroad bridge and through the city, then curves north by a series of industrial ponds as well as First, Second, Third, and Fourth lakes, which are on the right. At RM 113 (RK 182), Wilson Lake is on the right, and about further downstream, the Willamette leaves Benton County and becomes the boundary between Linn County, on the right, and Polk County on the left. Roughly later, the river leaves Linn County and becomes the boundary between Polk County on the left and Marion County on the right. The Santiam River enters from the right from the Willamette's mouth, and the Luckiamute River enters from the left slightly below the mouth of the Santiam. About later, the river reaches Buena Vista County Park and the unincorporated community of Buena Vista, both on the left, and the Buena Vista Ferry, which carries vehicles using Buena Vista Road between Polk and Marion counties. Below the ferry crossing, the river goes around Wells Island and receives Rock Creek from the right at RM 104 (RK 167). Through the next stretch, Ankeny National Wildlife Refuge is on the right. The river then passes Tyson Island and Murphy Bar before passing under a bridge carrying River Road South in Independence, where Riverview Park is on the left about from the mouth. Ash Creek, which flows through Independence, enters from the left.Williams, p. 115
Fuller Creek enters from the right about later. About further downstream, Dove's Bar is on the right and Hayden Island on the left before Rickreall Creek enters from the left. Over the next stretch, Oregon Route 22 and the Union Pacific Railroad are on the left. Holman State Wayside is on the left and Minto-Brown Island Park is on the right. At RM 85 (RK 137), the river passes the neighborhood of West Salem, which is on the left, while the main part of the city of Salem is on the right. Slightly downstream on the right is a USGS gauging station, below which the Willamette flows under the Center Street Bridge and then the Marion Street Bridge, which carry Oregon Route 22 eastbound and westbound, respectively. Then Mill Creek enters from the right, opposite Wallace Marine Park. Still in Salem, the river flows by River Road City Park and Rivers Edge Park, both on the right. North of Salem, the river passes the city of Keizer, which is on the right, before receiving Glenn Creek from the left about from the mouth. On the right at this point is Keizer Rapids Park, and slightly downstream on the left is Darrow Rocks. Over the next stretch, Oregon Route 221 runs roughly parallel to the river and on its left.Williams, p. 129