page_title: McKenzie River (Oregon)
section_title: Watershed
hierarchical_section_title: McKenzie River (Oregon) / Watershed
caption_attribution_description: English: Cougar Dam on the South Fork McKenzie River near Blue River, Oregon, USA. USACE Cougar Dam website
context_page_description: The McKenzie River is a 90-mile tributary of the Willamette River in western Oregon in the United States. It drains part of the Cascade Range east of Eugene and flows westward into the southernmost end of the Willamette Valley. It is named for Donald McKenzie, a Scottish Canadian fur trader who explored parts of the Pacific Northwest for the Pacific Fur Company in the early 19th century. As of the 21st century, six large dams have been built on the McKenzie and its tributaries.
context_section_description: The McKenzie River drains a region of about 1,300 square miles (3,400 km²) and is one of the primary tributaries of the Willamette River. Elevations in the watershed range from 10,358 feet (3,157 m) at the summit of the South Sister to 375 feet (114 m) at the McKenzie's mouth on the Willamette River north of Eugene. The upper basin, in the high Cascades, consists of granular, permeable igneous rocks that are geologically young, while most of the middle and lower McKenzie valley in the Western Cascades is made of the remnants of older, more weathered volcanic rocks. Major watersheds bordering the McKenzie basin include the Calapooia; the South, Middle and North Santiam rivers to the north; the Middle Fork Willamette River to the south; and the Deschutes River to the east.
  Most of the watershed is lightly populated; about 70 percent of it is public land managed by the U.S. Government, of which about 39 percent is the Three Sisters Wilderness. Over 96 percent of the basin is forested, just under 4 percent is devoted to agricultural use—mainly farms and orchards on the lower floodplain—and the remainder is residential or industrial. Most of the public land is part of the Willamette National Forest and is important for logging and recreation. The river is the sole tap water source for the cities of Eugene and Springfield, fulfilling the water needs of about 200,000 people. The Eugene Water & Electric Board (EWEB) utility draws the water at river mile (RM) 11 or river kilometer (RK) 18 in Springfield. Water quality in the river is rated good to excellent, with better quality upstream than downstream. Principal sources of contaminants in the McKenzie are agriculture and residential development, including septic systems. Small amounts of herbicides detected in the river and some of its tributaries may be from aerial spraying by timber companies for forestry.
  The region has a temperate climate with wet winters and dry summers. About 90 percent of precipitation in the watershed comes between October and May. Precipitation in the basin varies greatly with elevation; about 40 inches (1,000 mm) fall annually in the Willamette Valley, while the Three Sisters in the high Cascades can receive 125 inches (3,200 mm) in a year. Above 4,000 feet (1,200 m), about 35 percent of precipitation falls as snow, and at 7,000 feet (2,100 m) and higher, over 75 percent of precipitation is snowfall. At these elevations, melting snow beginning in the spring season brings more cold water out of springs under the permeable rock, increasing the McKenzie's flow and maintaining cold water temperatures in the river and its tributaries. Along the lower McKenzie, however, winter rain slides easily off the less permeable rock and erodes sediment into the river.
caption: Cougar Dam and reservoir on the South Fork McKenzie River
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