Weeks Falls, Cascading waterfall in King County, United States

Weeks Falls is a waterfall in King County featuring multiple drops along the South Fork of the Snoqualmie River. Water cascades over steep terrain creating layers of falling water and white spray throughout the descent.

Weeks Falls is a single cascade of about 18 metres high and 9 metres wide on the South Fork Snoqualmie River. A small run-of-the-river hydroelectric plant was built here without a dam: water is drawn from the river above the falls and carried through an underground channel to a single 4.3 MW generating unit at the foot of the falls. As of year-end 2024 the plant produced 13.1 GWh annually.

The falls sit at the end of the road past the Olallie State Park ranger headquarters, and a paved overlook by the gravel parking lot gives a view of both the cascade and the small powerhouse area. A quarter-mile accessible interpretive trail nearby explains the site.

Access requires taking Interstate 90 to exit 38 and then following a gravel path. Wear sturdy shoes since the ground can be slippery, especially after rain.

The hydro plant here works without a dam: water is diverted from the river above the falls and carried through an underground channel to a single 4.3 MW generating unit at the base, which produced 13.1 GWh in 2024.