<Tr> <Th> Islands </Th> <Td> Wizard Island Phantom Ship </Td> </Tr> <Tr> <Td_colspan="2"> Shore length is not a well - defined measure . </Td> </Tr> <P> Crater Lake (Klamath: giiwas) is a caldera lake in south - central Oregon in the western United States . 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 . With a depth of 1,949 feet (594 m), the lake is the deepest in the United States . In the world, it ranks ninth for maximum depth, and third for mean (average) depth . </P> <P> Crater Lake is 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 . </P>

Where does crater lake's water come from