|This article needs additional citations for verification. (January 2010)|
View of the ancient landslide that dammed Lake Crescent
|Location||Clallam County, Washington|
|Primary inflows||Barnes Creek, Smith Creek, Aurora Creek, Eagle Creek|
|Primary outflows||Lyre River|
|Basin countries||United States|
|Max. length||12 mi (19 km)|
|Surface area||5,127-acre (21 km2)|
|Average depth||300 ft (91 m)|
|Max. depth||624 ft (190 m) officially;
over 1,000 ft (300 m) unofficially
|Surface elevation||580 ft (180 m)|
Lake Crescent is a deep lake located entirely within Olympic National Park in Clallam County, Washington, United States, approximately 17 miles (27 km) west of Port Angeles, Washington on U.S. Route 101 and nearby to the small community of Piedmont. At an official maximum depth of 624 feet (190 m), also the maximum depth of the depth sounder used to find that depth (see depth section), it is officially the second deepest lake in Washington. Unofficial depth measurements of more than 1,000 feet (300 m) have been recorded.
Lake Crescent is known for its brilliant blue waters and exceptional clarity, caused by a lack of nitrogen in the water which inhibits the growth of algae. It is located in a popular recreational area which is home to a number of trails, including the Spruce Railroad Trail, Pyramid Mountain trail, and the Barnes Creek trail to Marymere Falls. The Spruce Railroad Trail follows the grade of what was once the tracks of a logging railroad along the shores of the lake. Following this trail on the north side of the lake, one can find the entrance to an old railroad tunnel as well as "Devils Punch Bowl", a popular swimming and diving area.
The lake was formed when glaciers carved out deep valleys during the last Ice Age. Initially, the Lake Crescent valley drained into the Indian Creek valley and then into Elwha River. Anadromous fish such as steelhead and coastal cutthroat trout migrated into the valley from lower waters.
Approximately 8,000 years ago, a great landslide from one of the Olympic Mountains dammed Indian Creek and the deep valley filled with water. Many geologists believe that Lake Crescent and nearby Lake Sutherland formed at the same time, but became separated by the landslide. The results of the landslide are easily visible from the summit of Pyramid Mountain. Eventually, the water found an alternative route out of the valley, spilling into the Lyre River, over the Lyre River Falls, and out to the Strait of Juan de Fuca.
The anadromous fish populations in the lake became landlocked, because those fish could not ascend Lyre River Falls, making a barrier in that direction. Over time, two different subspecies of fish evolved in the lake: the endemic Beardslee trout, a relative of rainbow trout, spawns in the Lyre River above the falls, while the Crescenti Cutthroat Trout spawns in Barnes Creek.
In the early 1960s, the U.S. Navy did a survey of the lake using a Furuno depth sounder. They were not able to verify the maximum depth on their equipment. During a 1970 depth survey conducted by the students of the fisheries program at Peninsula College in Port Angeles, Washington, students used instruments that could not record measurements beyond a depth of 624 feet, which thus became the "official" depth of the lake as recorded by the National Park Service. However, when power cable was being laid in the lake, instruments showed depths in excess of 1000 feet, the maximum range of the equipment used. The actual maximum depth of Lake Crescent remains unknown.
It is not certain whether the lake was named for its crescent shape or for its proximity to Crescent Bay, which was named by Henry Kellett in 1846. In 1849 two British–Canadian fur trappers, John Sutherland and John Everett, forged inland from Crescent Bay. The two lakes they found became known as Lake Sutherland and Everett Lake. Later, Everett Lake was renamed Lake Crescent. It has also been known as Big Lake and Elk Lake.
In 1890, while the Port Crescent Improvement Company was promoting its townsite near the lake, M.J. Carrigan started the Port Crescent Leader to help boost the town. He wrote of the beautiful lake, which he called Lake Crescent, and the name soon became well established.
In 1929, Russell and Blanch Warren disappeared while driving in the vicinity of Lake Crescent. Their whereabouts remained unknown until 2002, when their 1927 Chevrolet automobile was found over 160 feet beneath the surface of Crescent Lake. 
- Williams, p.145
- Parratt, Smitty (1984). Gods & goblins: A Field Guide to Place Names of Olympic National Park. CP Publications. pp. 82–83. ISBN 0-914195-00-X.
- Meany, Edmond S. (1920). "Origin of Washington Geographic Names". The Washington Historical Quarterly (Washington University State Historical Society) XI: 53. Retrieved 2009-06-11.
- "LAKE CRESCENT MYSTERY - Olympic National Park". Windsox.us. Retrieved 2013-07-08.
- Williams, Hill. The Restless Northwest: A Geological Story, Washington State University Press, 2002, ISBN 0-87422-250-8.
Media related to Lake Crescent at Wikimedia Commons
- Olympic National Park (National Park Service)
- The allure of Lake Crescent never grows old Article from the Seattle Post-Intelligencer.
- The Evergreen Playground University of Washington Libraries Digital Collections. Online museum exhibit that highlights the history of tourism on the Olympic Peninsula, including the development of the Olympic Loop Highway (U.S. Highway 101) and the Olympic National Park. Includes many images of Lake Crescent.
- History Around Lake Crescent, Clallam County, Washington By Andrew Craig Magnuson.