The Upper Truckee River is a stream that flows northward from the western slope of Red Lake Peak in Alpine County, California to Lake Tahoe via the Truckee Marsh in South Lake Tahoe, California. The river flows northeasterly and is 23 miles (37 km) long. It is Lake Tahoe's largest tributary.
This watershed is the largest in the Lake Tahoe Basin and occupies 56.5 square miles (146 km2), which is 18 percent of the total land area tributary to Lake Tahoe (314 square miles (810 km2)). Tributaries include Angora, Echo, Grass Lake, and Big Meadow Creeks, and Upper and Lower Echo, Round, and Dardanelles Lakes. Major lakes include and smaller lakes include Dardanelles, Round, Showers, Elbert, Tamarack, Ralston, and Angora Lakes. The stretch between Meyers and South Lake Tahoe is known as Lake Valley.
Historically, Trout Creek was tributary to Upper Truckee River in the Truckee Marsh area near the lake. But with development of the Tahoe Keys, the Upper Truckee River was channeled to the lake and currently the streamflow of the two tributaries combine only during high runoff.