induced changes have interacted synergistically with certain natural factors, ameliorating some of these factors and exacerbating others. This chapter discusses key environmental and human features in the Columbia River basin and how human activities have impacted the basin’s environmental systems. The basin’s complex physical character and the changes induced by nineteenth- and twentieth-century agricultural, forestry, and industrial activities provide the context for considering more detailed aspects of changes to the Columbia River hydrological regime and its interactions with the life histories of Columbia River salmonids.

Most inhabitants of the Pacific Northwest live in the Port-land-Seattle urban corridor west of the Cascade Mountains (Portland lies within the Columbia River basin; Seattle does not). Of the roughly 9.5 million people in the four northwestern states (Idaho, Montana, Oregon, and Washington), about 5 million live in the Columbia River basin (Volkman, 1997). Like the rapidly growing Portland-Seattle corridor, the basin’s interior has experienced population growth in many areas since the 1980s, with the largest increases in the urban areas of Bend (Oregon), Boise (Idaho), Richland/Pasco/Kennewick (the “Tri-Cities”), Spokane, Wenatchee, and Yakima (these last four urban areas are in Washington State). Beyond these cities, the rest of the basin is only sparsely populated.

Humans have inhabited the Pacific Northwest for at least 15,000 years (Jackson and Kimerling, 2003). Early inhabitants made a transition from hunting large game to a more sedentary lifestyle about 3,500 years ago, and salmon became an important part of their sustenance and culture. Even then, human activities