Clear Lake is a mountain 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,...

 86 mi (138 km) northeast of Eugene, Oregon

Eugene, Oregon

Eugene is the second largest city in the U.S. state of Oregon and the seat of Lane County. It is located at the south end of the Willamette Valley, at the confluence of the McKenzie and Willamette rivers, about east of the Oregon Coast.As of the 2010 U.S...

, United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 in Linn County

Linn County, Oregon

Linn County is a county located in the U.S. state of Oregon. It is named in honor of Lewis F. Linn, a U.S. Senator from Missouri who advocated the American occupation of the Oregon Country. By the 2010 US census the population of Linn county was 116,672 showing a 13.2% growth since the 2000 census...

. It has two main bodies connected by a bottleneck. The lake is primarily fed by snow runoff from nearby Mount Washington

Mount Washington (Oregon)

Mount Washington is a deeply eroded shield volcano in the Cascade Range of Oregon. The mountain dates to the Late Pleistocene. However, it does have a line of basaltic andesite spatter cones on its northeast flank which are approximately 1,330 years old according to carbon dating...

 and the surrounding areas. The runoff filters through underground caverns for more than 20 years before emptying into Clear Lake. The lake is also fed by two small creeks which may dry up seasonally.

Clear Lake is the headwaters of the McKenzie River

McKenzie River

The McKenzie River is a tributary of the Willamette River in western Oregon in the United States. It drains part of the Cascade Range east of Eugene and flows into the southernmost end of the Willamette Valley. It is named for Donald MacKenzie, a Scottish Canadian fur trader...

, which is the sole source of drinking water for Eugene.

Diving in Clear Lake

Clear Lake is reported to be one of the most exceptional freshwater dive spots in the United States.
Submerged 100 feet (30.5 m) deep in the lake is a stand of upright trees that were killed approximately 3,000 years ago when volcanic activity created the lake. The trees are remarkably preserved due to the cold year-round water temperatures of between 35–43 °F (1.6–6 °C).