The Williamson River of south-central Oregon in the United States is about long. It drains about east of the Cascade Range. The lake's outlet is the Link River, which flows into Lake Ewauna and the Klamath River. ). It flows in a large arc north through the mountains, then west, then southwest through Klamath Marsh and the Klamath Marsh National Wildlife Refuge. Downstream of the refuge, the river flows roughly parallel to U.S. Route 97, receiving Spring Creek from the right at Collier Memorial State Park, about north of Chiloquin. At Chiloquin, it receives the Sprague River from the left at about river mile (RM) 11 (river kilometer (RK) 18). The Williamson enters the northern end of Upper Klamath Lake near Modoc Point, about northwest of Klamath Falls.
Watershed
At lower elevations along big streams, the Williamson watershed supports irrigated pastures and other farmlands. Livestock grazing occurs in many locations in the basin. Forests, often cut for timber, cover about 81 percent of the basin and farms account for 6 percent, while range, wetlands, water, and urban areas cover a combined 13 percent. Precipitation in the basin, which lies in the rain shadow of the Cascade Range, averages a year along the Williamson above its confluence with the Sprague and about along the Sprague. Smaller numbers of brown trout also thrive in the Williamson, especially below Spring Creek. Lost River suckers also populate the river but are protected and cannot be caught and kept legally. Smaller rainbow trout and brook trout live in the river above Klamath Marsh. Much of the land along the river is privately owned, and public access is limited.
In early Pleistocene times, the Klamath Marsh and Upper Klamath lake were much larger; and were maintained as shallow lakes and marshes by the continued subsidence of the basin in the face of abundant sedimentation and uplift along the eastern fault scarp. The eruption of Mount Mazama about 7,700 years ago contributed an enormous amount of sediment to the lake and marsh basins, and filled the canyon of the Williamson River.
thumb|The Williamson River southwest of Chiloquin
See also
- List of longest streams of Oregon