The Willamette Falls is a natural waterfall on the Willamette River between Oregon City and West Linn, Oregon, in the United States. It is the largest waterfall in the Northwestern United States by volume, and the seventeenth widest in the world. Horseshoe in shape, it is 1,500 feet (460 m) wide and 40 feet (12 m) high with a flow of 30,849 cu ft/s, located 26 miles (42 km) upriver from the Willamette's mouth. Willamette Falls is a culturally significant site for many tribal communities in the region.

The Willamette River is a major tributary of the Columbia River, accounting for 12 to 15 percent of the Columbia's flow. The Willamette's main stem is 187 miles (301 km) long, lying entirely in northwestern Oregon in the United States. Flowing northward between the Oregon Coast Range and the Cascade Range, the river and its tributaries form the Willamette Valley, a basin that contains two-thirds of Oregon's population, including the state capital, Salem, and the state's largest city, Portland, which surrounds the Willamette's mouth at the Columbia.