Crater Lake was a caldera lake in the western United States, located in south-central Oregon. It is the main feature of Crater Lake National Park and is famous for its deep blue color and water clarity. The lake partly fills a nearly 2,148-foot (655 m)-deep caldera that was formed around 7,700 (± 150) years ago by the collapse of the volcano Mount Mazama. There are no rivers flowing 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 250 years. At 1,943 feet (592 m), the lake is the deepest in the United States, and the seventh or ninth deepest in the world, depending on whether average or maximum depth is measured.
Crater Lake was also known for the "Old Man of the Lake", a full-sized tree which is now a stump that has been bobbing vertically in the lake for over a century. The low temperature of the water has slowed the decomposition of the wood, hence the longevity of the bobbing tree.
Two islands are in Crater Lake; Wizard Island formed from a cinder cone that erupted after Crater Lake began to fill with water, and the smaller Phantom Ship has seven different trees living on it. There are also colonies of violet green swallows and several varieties of wildflowers and lichens living there.
While having no indigenous fish population, the lake was stocked from 1888 to 1941 with a variety of fish. Several species have formed self-sustaining populations.