Ardeth Lake is an alpine lake in Boise County, Idaho, United States, located high in the Sawtooth Mountains in the Sawtooth National Recreation Area. The lake is approximately 18 miles (29 km) south of Stanley. Ardeth Lake is most easily accessed from trailheads in the Sawtooth Valley, which are accessed from State Highway 75 or from the Grandjean trailhead to the northwest off of State Highway 21.