Crater Lake is a caldera

Caldera

A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...

 lake

Lake

A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

 located in the south-central region of the U.S. state

U.S. state

A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...

 of Oregon

Oregon

Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...

. It is the main feature of Crater Lake National Park

Crater Lake National Park

Crater Lake National Park is a United States National Park located in southern Oregon. Established in 1902, Crater Lake National Park is the sixth oldest national park in the United States and the only one in the state of Oregon...

 and famous for its deep blue color and water clarity. The lake partly fills a nearly 2148 feet (654.7 m) deep caldera that was formed around 7,700 (± 150) years ago
by the collapse of the volcano Mount Mazama

Mount Mazama

Mount Mazama is a destroyed stratovolcano in the Oregon part of the Cascade Volcanic Arc and the Cascade Range. The volcano's collapsed caldera holds Crater Lake, and the entire mountain is located within Crater Lake National Park....

. 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.

On June 12, 1853, John Wesley Hillman

John Wesley Hillman

John Wesley Hillman was an American prospector during the California Gold Rush and explorer who was among the first European Americans to see Crater Lake in the U.S. state of Oregon....

 was reportedly the first person of European descent to see what he named "Deep Blue Lake" in Oregon.