Pend Oreille Lake, a lake in northern Idaho. It is the largest lake in the state, with a length of 40 miles (65 km), an average width of 4 miles (6 km), a maximum depth of 1,200 feet (366 m), and a surface area of 148 square miles (383 km2). The Clark Fork River enters the lake on the east, and becomes the Pend Oreille River, a tributary of the Columbia, when it leaves on the west.