Crater Lake is the U.S. lake inside the volcanic caldera in Oregon’s Crater Lake National Park.
The caldera formed when Mount Mazama, a large Cascade volcano, collapsed after a colossal eruption roughly 7,700 years ago. Rain and snowfall gradually filled the depression, creating a remarkably clear, intensely blue lake with no rivers flowing in or out.
At 1,949 feet, Crater Lake is the deepest lake in the United States. Its water balance depends almost entirely on precipitation, evaporation, and underground seepage; the lake’s water is replaced over roughly 150 years.
A common mix-up is confusing the lake with the park. Crater Lake is the natural feature, while Crater Lake National Park, established in 1902, protects it and the surrounding volcanic landscape. Wizard Island is a cinder cone rising from the lake.