Bull Run River (Oregon)

The Bull Run River is a tributary of the Sandy River in the U.S. state of Oregon. Beginning at the lower end of Bull Run Lake in the Cascade Range, it flows generally west through the Bull Run Watershed Management Unit (BRWMU), a restricted area meant to protect the river and its tributaries from contamination. The river, impounded by two artificial storage reservoirs as well as the lake, is the primary source of drinking water for the city of Portland, Oregon.

It is likely that Native American living along the Columbia River as early as 10,000 years ago visited the Bull Run watershed in search of food. More recently they created trails over the Cascade Range and around Mount Hood, near the upper part of the Bull Run watershed. By the mid-19th century, pioneers used these trails to cross the mountains from east to west to reach the fertile Willamette Valley. In the 1890s, the City of Portland, searching for sources of clean drinking water, chose the Bull Run River. Dam-building, road construction, and legal action to protect the watershed began shortly thereafter, and Bull Run water began to flow through a large pipe to the city in 1895.

Erosion-resistant basalt underlies much of the watershed, and streams passing over it are relatively free of sediments. However, turbidity increases when unstable soils sandwiched between layers of basalt and other volcanic rocks are disturbed and wash into the river during rainstorms. Despite legal protections, about...
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