Crater Lake is a volcanic crater lake in south-central Oregon in the Western United States. It is the main feature of Crater Lake National Park and is a tourist attraction for its deep blue color and water clarity. The lake partly fills a 2,148-foot-deep caldera that was formed around 7,700 years ago by the collapse of the volcano Mount Mazama. No rivers flow int…Crater Lake is a volcanic crater lake in south-central Oregon in the Western United States. It is the main feature of Crater Lake National Park and is a tourist attraction for its deep blue color and water clarity. The lake partly fills a 2,148-foot-deep caldera that was formed around 7,700 years ago by the collapse of the volcano Mount Mazama. No rivers flow into or out of the lake; the evaporation is compensated for by rain and snowfall at a rate such that the total amount of water is replaced every 150 years. With a depth of 1,949 feet, the lake is the deepest in the United States. In the world, it ranks tenth for maximum depth, as well as third for mean depth.