Crater Lake is a caldera lake located in the south-central region of the U.S. state of Oregon. It is the main feature of Crater Lake National Park and 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.
On June 12, 1853, John Wesley Hillman was reportedly the first person of European descent to see what he named "Deep Blue Lake" in Oregon. The lake was renamed at least three times, as Blue Lake, Lake Majesty, and finally Crater Lake.
Crater Lake is 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 more than a century. The low temperature of the water has slowed the decomposition of the wood, hence the longevity of the bobbing tree.
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.
Crater Lake is located in Klamath County, approximately 60 miles (97 km) northwest of the county seat of Klamath Falls, and about 80 miles (130 km) northeast of the city of Medford.
The lake is 5 by 6 miles (8 by 10 km) across with an average depth of 1,148 feet (350 m). Its maximum depth has been measured at 1,949 feet (594 m), which fluctuates slightly as the weather changes. On the basis of maximum depth, Crater Lake is the deepest lake in the United States, the second deepest in North America, after Great Slave Lake in Canada, and the ninth deepest lake in the world (Lake Baikal is the deepest). Crater Lake is often cited as the seventh deepest lake in the world, but this ranking excludes Lake Vostok, which is situated under nearly 13,000 feet (4,000 m) of Antarctic ice, and the recent soundings of San Martín Lake, which is located on the border of Chile and Argentina.
However, on the basis of comparing average depths among the world's deepest lakes, Crater Lake becomes the deepest lake in the Western Hemisphere and the third deepest in the world. Comparing average depths among the world's lakes whose basins are entirely above sea level, Crater Lake is the deepest.
The caldera rim of Crater Lake ranges in elevation from 7,000 to 8,000 feet (2,100 to 2,400 m).