Lake Pend Oreille ( ) in the northern Idaho Panhandle is the largest lake in the U.S. state of Idaho and the 38th-largest lake by area in the United States, with a surface area of . It is long, and deep in some regions, making it the fifth-deepest in the nation. The lake is fed by the Clark Fork River and the Pack River, and drains into the Pend Oreille River, as well as subsurfacely into the Spokane Valley–Rathdrum Prairie Aquifer.