Alturas Lake, Glacial lake in Sawtooth Valley, Idaho, US.

Alturas Lake is a glacial lake in the Sawtooth Valley of Blaine County, Idaho, about 21 miles (34 km) south of Stanley and 30 miles (48 km) northwest of Ketchum. It is the second largest lake in the Sawtooth National Recreation Area, reached from State Highway 75 via Sawtooth National Forest road 205. Leah Lake and Logjam Lake lie upstream, and the northern shore has easy access, several campgrounds and private camps.

Alturas Lake takes its name from Alturas County, a defunct administrative division of Idaho's territorial era. The lake lies in Blaine County, into which the old county was later reorganized. The name stayed with the lake after the county itself disappeared.

The name comes from Alturas County, a defunct Idaho county, not from any local feature. The northern shore is the easiest to reach and holds several campgrounds plus private camps, while Leah Lake and Logjam Lake lie upstream. The lake is the second largest in Sawtooth National Recreation Area.

Alturas Lake is reached from State Highway 75 via Sawtooth National Forest road 205, which runs to the northern shore. The northern shore has easy access, several campgrounds and private camps. Leah Lake and Logjam Lake lie upstream of Alturas Lake.

Alturas Lake is the second largest lake in Sawtooth National Recreation Area, after Redfish Lake, and Leah Lake and Logjam Lake lie upstream of it. It takes its name from the defunct Alturas County, Idaho, a territorial-era division later reorganized into present-day Blaine County.