Crater Lake National Park is one of the oldest parks in the United States, created in 1902 by President Theodore Roosevelt. The first lodge in the park opened in 1915, and the Rim Drive around the lake gave the public easy access to the entire lake in 1918. Soundings of the lake show it is exceedingly deep, reaching as low as 1,943 feet (592 meters), making it the deepest lake in the United States. The lake is in the former caldera of Mount Mazama, which erupted around 7,700 years ago.

The rim wall of Crater Lake is a natural barrier over which no river reaches. All the water in the lake comes from rainfall or snow that fell directly into the crater and accumulated over time.