The deepest lake in the United States, famous for its clarity, is Crater Lake.
Crater Lake lies in southern Oregon inside the caldera of Mount Mazama, a volcano that collapsed after a major eruption about 7,700 years ago. The lake reaches a maximum depth of 1,949 feet, making it the deepest lake in the United States and the second-deepest in North America after Canada's Great Slave Lake.
Its striking blue color and clarity come partly from its unusual water source. No rivers flow into the lake; rain and snow provide nearly all of its water, while evaporation and underground seepage remove it. With little sediment entering from streams, the water can be exceptionally transparent. A 1997 measurement recorded visibility to about 142 feet using a Secchi disk.
Crater Lake is sometimes confused with a lake occupying a simple volcanic crater, but it actually fills a much larger caldera created by collapse. It also contains Wizard Island, a cinder cone that formed after the caldera developed. The lake became the centerpiece of Crater Lake National Park, established in 1902, Oregon's only national park.