Lake Coeur d'Alene, officially Coeur d'Alene Lake ( ), is a natural dam-controlled lake in North Idaho, located in the Pacific Northwest region of the United States. At its northern end is the city of Coeur d'Alene. It spans in length and ranges from 1 to wide with over of shoreline. The lake was named after the Coeur d'Alene people. Geology and geography Lake Coeur d'Alene, like other lakes surrounding the Spokane Valley and Rathdrum Prairie, was formed by the Missoula Floods, most recently 12,000 to 15,000 years ago. The Purcell Lobe of the Cordilleran Ice Sheet flowed south from Canada, carving the basin of present-day Lake Pend Oreille and damming the Clark Fork river. The impounded river repeatedly filled to form Glacial Lake Missoula and broke through the ice dam, resulting in massive floods that filled the Rathdrum Prairie area with sand, gravel, and boulders. Large eddy bars formed downstream from bedrock obstructions, thereby damming tributary valleys and creating lakes. Lake Coeur d'Alene is fed primarily by two rivers, the Coeur d'Alene and the Saint Joe. The outflow is via the Spokane River. The lake's elevation varies from above sea level in the summer to up to lower in the winter, controlled by the Post Falls Dam below the lake on the Spokane River. The lake's average surface temperature between June 1 and September 30 is . History The first-recorded European to see the area was explorer David Thompson in 1807. Flooding as a result of the construction and operation of the Post Falls Dam drastically changed the shape and size of the lake, expanding it to combine several smaller lakes into one. The lake has been used for transporting lumber by water in Kootenai County since the timber industry started in the region. Prior to a fire in 1917, Harrison was planned as the county seat of Kootenai County, as the swiftly growing lumber town was at an opportune junction of the St. Joe and Coeur d' Alene rivers. After the fire, the mills were moved mostly to the city of Coeur d'Alene, which developed more and was designated as the county seat. A number of Ford Model T automobiles sitting on the bottom of the lake are the result of people in the early 1900s choosing to drive in winter across the frozen lake. But they did not always judge how thick the ice was, and went