Columbia Slough - Course

Course

The Columbia Slough flows roughly parallel to and about 0.4 to 1.7 miles (0.6 to 2.7 km) south of the Columbia River in Multnomah County. It begins at Fairview Lake in the city of Fairview and immediately enters the city of Gresham. Less than 1 mile (1.6 km) later, it enters the city of Portland and continues generally westward for about another 18 miles (29 km) to its confluence with the Willamette River. Throughout its course, the slough is nearly level, 10 feet (3.0 m) above sea level at the source and 9 feet (2.7 m) at the mouth. Semidiurnal tides cause reverse currents on the lower 8.5 miles (13.7 km) of the slough.

Running slightly north of and parallel to U.S. Route 30 (Sandy Boulevard), the slough flows by Zimmerman Heritage Farm on the left bank (south) about 17.5 miles (28.2 km) from the mouth, Big Four Corners Wetlands on the right bank shortly thereafter, and receives Wilkes Creek on the left shortly after that. At about river mile (RM) 15.5 or river kilometer (RK) 24.9, it passes through a gated levee that separates the upper slough from the middle slough. Soon it passes Prison Pond Wetlands near Inverness Jail and connects to Johnson Lake Slough, all on the left. Shortly thereafter, it flows under Interstate 205. From here and for most of the rest of its course, the slough runs parallel to and slightly north of Columbia Boulevard. Passing Johnson Lake on the left, it crosses the Colwood National Golf Course and flows by Portland International Airport and an Oregon Air National Guard base on the right. On the left is Whitaker Ponds Natural Area. Shortly thereafter, it receives Whitaker Slough on the left and crosses the Broadmoor Golf Course. Between 9 and 8 miles (14 and 13 km) from the mouth, it receives Buffalo Slough from the left and passes by the defunct Peninsula Drainage Canal (City Canal), which lies to the slough's right. At this point, it passes through a second gated levee that separates the middle slough from the lower slough and its tidal flow reversals.

In the next stretch, the Columbia Slough flows by Portland Meadows horse racing track on the right and crosses under Interstate 5 at about RM 7 (RK 11). Beyond the interstate, to the slough's north lies Delta Park, Portland International Raceway, and the Heron Lakes Golf Course. Until flooding destroyed it in 1948, the city of Vanport occupied this site. To the south is the Columbia Boulevard Wastewater Treatment Plant.

The slough flows through the Wapato Wetland and by the Smith and Bybee Wetlands Natural Area, including the former St. Johns Landfill, on the right at about RM 3 (RK 4.8) from the Willamette River, and by Pier Park on the left. Shortly thereafter, it turns sharply north for the rest of its course. It receives North Slough, connected to Bybee Lake, on the right, and passes through the Ramsey Lake Wetlands and Kelley Point Park before entering the Willamette River about 1 mile (1.6 km) from its confluence with the Columbia River. The mouth of the Columbia River is about 101 miles (163 km) further downstream at Astoria on the Pacific Ocean.