The Spokane River flows 111 miles from Lake Coeur d’Alene, Idaho, to Lake Roosevelt, which is the Columbia River impounded by Grand Coulee Dam. The lower 29 miles of the Spokane River is known as the Spokane Arm of Lake Roosevelt. The river basin is about 2,400 square miles in size. The Spokane River’s entire drainage basin is about 6,240 square miles large, of which 3,840 square miles are above Post Falls Dam at the outlet of Coeur d’Alene Lake. Its mean annual discharge is 7,946 cubic feet per second.
From Lake Coeur d’Alene, the Spokane River traverses the Rathdrum Prairie until reaching Post Falls, Idaho where it passes over a dam, and a natural 40-foot waterfall. Continuing westward, it later passes over 5 more dams, four of which are located in the city of Spokane. In Spokane, it flows over the Spokane Falls, which are located in the heart of Downtown Spokane, approximately one third of the way down the rivers length. About a mile later, the river receives Latah Creek from the southeast. Soon afterwards, it is met from the northeast by the Little Spokane River, on the western edge of the city of Spokane. It flows in a zigzag course along the southern edge of the Selkirk Mountains, forming the southern boundary of the Spokane Indian Reservation, where it is impounded by the Little Falls Dam to form Long Lake, a 15 mi (24 km) reservoir. It joins Franklin D. Roosevelt Lake on the Columbia from the east at Miles. The site of historic Fort Spokane is located at the mouth of the river on the Columbia.
The Spokane has three major tributaries: the Little Spokane River and Hangman (also called Latah) Creek, both in the Spokane area; and Chamokane (also called Tshimikain by the Spokane Tribe of Indians) in the lower part of the basin. The Spokane River Basin includes parts of five Washington counties — Pend Oreille, Stevens, Lincoln, Spokane, and Whitman — and three Idaho counties, Benewah, Kootenai, and Bonner.
There are seven dams on the Spokane, from Post Falls Dam at the outlet from Lake Coeur d’Alene to Little Falls Dam at river mile 29. All have hydroelectric generators. One, Upriver Dam, is owned and operated by the City of Spokane Water Department, and the others are owned by Avista Corp., an electricity and natural gas utility based in Spokane. The dams were built between 1890 and 1922. None has fish-passage facilities. Little Falls Dam, completed in 1911 at river mile 29, stopped the fish from returning farther upstream. The dam was built with a fish ladder, but it did not work well. The much larger Long Lake Dam, completed in 1915 five miles upstream, had no fish ladder. Salmon continued to spawn downriver from Little Falls Dam into the late 1930s, when Grand Coulee Dam, then under construction, blocked all salmon and steelhead from the upper Columbia River Basin.