Columbia Slough

The Columbia Slough is a narrow waterway, about 19 miles long, in the floodplain of the Columbia River in the U.S. state of Oregon. From its source in the Portland suburb of Fairview, the Columbia Slough meanders west through Gresham and Portland to the Willamette River, about 1 mile from the Willamette's confluence with the Columbia. It is a remnant of the historic wetlands between the mouths of the Sandy River to the east and the Willamette River to the west. Levees surround much of the main slough as well as many side sloughs, detached sloughs, and nearby lakes. Drainage district employees control water flows with pumps and floodgates. Tidal fluctuations cause reverse flow on the lower slough.

The Columbia floodplain, formed by geologic processes including lava flows, volcanic eruptions, and the Missoula Floods, is part of the Portland Basin, which extends across the Columbia River from Multnomah County, Oregon, into Clark County, Washington. Five percent of Oregon's population, about 158,000 people, live in the slough watershed of about 51 square miles . Municipal wells near the upper slough provide supplemental drinking water to Portland and nearby cities. The cities, the drainage districts, the county, and a regional government, Metro, have overlapping jurisdictions in the watershed. A regional agency operates Portland International Airport along the middle slough and marine terminals near the lower slough. The Oregon Department of Environmental Quality and the city's Bureau of Environmental Services deal with environmental issues.

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