The North Umpqua River is a tributary of the Umpqua River, approximately 100 miles long. It drains a scenic and rugged area of the Cascade Range southwest of Eugene, flowing through steep canyons and surrounded by large Douglas-fir forests. Renowned for its emerald green waters, it is considered one of the best fly fishing streams in the Northwest for anadromous fish.
It rises in the high Cascades, issuing from Maidu Lake at elevation of 5,980 feet in the Mount Thielsen Wilderness, along the Douglas-Klamath county line approximately 70 miles east of Roseburg. It follows a serpentine course down from the Cascades, westward along the southern side of the Calapooya Mountains. Its upper course passes through the Umpqua National Forest, past Toketee Falls and Steamboat, where it receives Steamboat Creek from the north. It receives the Little River from the south at Glide and joins the South Umpqua from the east approximately 5 miles northwest of Roseburg to form the Umpqua.
It is impounded in its upper reaches in the Cascades to form Lemolo Lake for hydroelectricity. It is also impounded for hydroelectricity at Soda Springs Dam, forming a small reservoir on the upper river.
The river's reputation as a world-class steelhead stream and its famous emerald waters are a result of the fact the river source is high enough in the Cascades to derive from snowmelt during the entire year. The melting snow is trapped in volcanic soil and pumice and released during the summer months, providing an even cool-temperature flow. During the summer the flow of the river is approximately 20 times that of the nearby South Umpqua. In its lower reaches, the river's flow becomes increasingly erratic, in a manner typical of mountain streams of the region.
The region around the river has long been a timber-producing area. Starting in 1955, the watershed of the river was extensively clear cut, a practice which continued until 1969 when forestry management practices were changed. During this period many tributary streambeds were used as impromptu logging roads. The recovery of the river from these practices has been closely monitored by state and federal agencies
OR 138 leaves Roseburg on the North Umpqua Highway No. 138 as it follows the Umpqua River's north fork. It heads due east out of Roseburg, ascending into the Cascade mountains, and turning northeast. Eventually, the highway turns south and reaches Diamond Lake, passing by the lake to the east. Just south of there is an intersection with Oregon Route 230, which bypass Crater Lake National Park to the west. South of there lies the north entrance to the park. OR 138 continues east from the entrance, descending into Central Oregon, and terminates at an intersection with U.S. Route 97 at Diamond Lake Junction, south of the town of Chemult.
The portion of the highway between Roseburg and Diamond Lake is part of the Rogue-Umpqua Scenic Byway. The portion between former Route 209 and US 97 is part of the Volcanic Legacy Scenic Byway.