Lake, Cascade Range , southwestern Oregon, U.S. The lake is in a huge volcanic caldera 6 mi (10 km) in diameter and 1,932 ft (589 m) deep.
It is the remnant of a mountain destroyed in an eruption more than 6,000 years ago. The intensely blue lake and its surrounding region became a national park in 1902; the park covers 250 sq mi (647 sq km).