Sylvan Lake is considered the “Crown Jewel” of Custer State Park in the Black Hills of western South Dakota . The mountain lake sits at the base of Harney Peak , the highest point east of the Rocky Mountains. Created in 1881 when Theodore Reder built a dam across Sunday Gulch, it offers picnic areas, rock climbing, small rental boats, swimming, and hiking trails. It is also popular as a starting point for excursions to Harney Peak and The Needles.

Sylvan Lake was featured in the 2007 movie “National Treasure: Book of Secrets.” Its location was depicted in the film as immediately behind the four faces of nearby Mount Rushmore National Memorial; however, it is actually five miles away.