Alpine Lake, Glacial lake in Sawtooth National Recreation Area, Idaho.

Alpine Lake is a glacial lake in the Sawtooth National Recreation Area, surrounded by rocky peaks and coniferous forests at high elevation. The water comes from snowmelt in the surrounding mountains and stays cold and clear throughout the year.

The lake basin was carved by glaciers during the last Ice Age, and it filled with meltwater as the ice retreated thousands of years ago. The landscape around it shows typical shapes created by ancient glacial movement.

The lake sits in the Sawtooth Wilderness, where a wilderness permit can be obtained at trailheads. Hikers reach it via a trail from the Redfish Lake Creek trailhead and campground, about 5 miles (8 km) along Redfish Creek to a junction, then up to the lake. Crossing Redfish Lake by boat shortens the approach by several miles.

Access is by hiking trail from trailheads in the recreation area, with routes taking several hours depending on starting point. The best season is late spring through early fall, when snow has melted and trails are passable.

Alpine Lake sits at 8,337 feet (2,541 m) and can stay frozen into early summer, so hikers may find ice well into the season. Packrat Peak, 10,240 feet (3,120 m), rises at the lake's southwestern end. Reaching the Redfish Lake trailhead can be shortened by taking a boat across Redfish Lake instead of hiking around it.