Discover the Oldest Lake in the United States!


Written by Jennifer Gaeng

Updated: May 12, 2023

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Clear Lake is a California lake north of Napa County and San Francisco. It’s the state’s largest natural freshwater lake, covering 68 square miles. At 2.5 million years old, Clear Lake is the United States and North America’s oldest lake. It is 1,417 ft above Lower Lake.

Clear Lake spans 68 square miles of the Golden State’s lush countryside. It used to be much larger and included the nearby Blue Lakes to the northeast, even though it is now a gigantic body of water. When at its widest, Clear Lake stretches for 19 miles and is 8 miles wide, covering 43,785 acres and holding 1,155,000 acre-feet of water.

Where is Clear Lake?

Clear Lake is located just an hour outside of California.

©Kim Joar Bekkelund / Creative Commons – Original / License

Clear Lake is a vast complicated lake that is an hour north of San Francisco. It’s California’s second-largest freshwater lake, after Lake Tahoe, and is fed by many streams and springs. Cache Creek runs east into the Central Valley as its only outflow. Upper Cache Creek Watershed feeds into the Sacramento River across Yolo County. Many of these mountains can be hiked or driven up via forest roads. Deep vegetation, woods, and private property are common off-track hazards. Mayacamas Mountains are on the west, and Cortina and Blue Ridge area on the east. St. John Mountain, Hull Mountain, and Snow Mountain are the northern high peaks in the southern Mendocino National Forest.

History Of Clear Lake Area

The San Andreas transform fault system, which connects the North American and Pacific plates, has many northwest-to-northwest-trending faults cutting across the region. About 3 million years ago, the San Andreas transform fault slid north behind the Mendocino triple junction, halting subduction at the Clear Lake latitude and leaving a slab window behind.

Crustal-silicic melt bubbled up as the Clear Lake Volcanics after subduction halted here. Volcanoes used to be all over the place, but today, they’re only visible near Clear Lake. The San Andreas regulates clear Lake’s volcanic vents and basins transform fault system. Displaced by faults, the pull-apart basin of Clear Lake was formed.

Can You Swim In Clear Lake?

Certain parts of Clear Lake are known to contain toxic blooms that humans and pets should avoid.

© Overstreet

You can swim in most parts of Clear Lake. However, toxic cyanobacteria blooms are in parts of Clear Lake. These toxic blooms pose a danger to human health and the local economy. State water inspectors have cautioned sailors to avoid Clear Lake’s eastern shore because of the risk of toxic blue-green algal blooms infecting humans and pets.

Unfortunately, in the 1990s, the lake was contaminated by the nearby Sulphur Bank Mercury Mine. A lot of people like catching and releasing; however, it’s best to avoid eating any fish caught in this area, especially for children and pregnant women. Although the lake is polluted, it nevertheless maintains a wide variety of aquatic species.

Recreational Activities

It is possible to find lodging and recreational activities despite the pollution in Clear Lake. With more than 100 miles of shoreline, Clear Lake is a popular vacation destination.


Sporting in the lake’s wide, warm water is excellent for a variety of water sports such as:

  • Sailing
  • Boat Racing
  • Water Skiing
  • Wakeboarding


Clear Lake is known as the “Bass Capital of the West.” Anglers there enjoy catching largemouth bass, which is cultivated and stocked by the California Department of Fish and Wildlife. Also available are:

  • Bluegill
  • Catfish
  • Crappie
  • Rainbow Trout

Vegetation and Wildlife

Most of the waterfront is constructed. However, parks, reserves, open water, and private land allow for nature observation. A variety of flora and fauna are abundant around and in Clear Lake, including:


  • Coots
  • Geese
  • Mallards
  • Mergansers
  • Ospreys
  • Plovers
  • Red-tailed hawks
  • Turkey vultures
  • Turkeys
  • Western grebes

Land Animals

Common Reptiles and Amphibians

Wrapping up the Oldest Lake in the United States

Clear Lake is one of the most interesting spots to visit on the west coast.


Clear Lake is not only the oldest lake in the United States but also one of the most interesting spots to visit on the west coast. It cannot be denied that Clear Lake holds a tremendous presence on this planet. Clear Lake’s natural beauty and wealth of wildlife, along with the state’s laid-back atmosphere, make it an ideal place to relax and unwind!

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About the Author

Jennifer Gaeng is a writer at A-Z-Animals focused on animals, lakes, and fishing. With over 15 years of collective experience in writing and researching, Jennifer has honed her skills in various niches, including nature, animals, family care, and self-care. Hailing from Missouri, Jennifer finds inspiration in spending quality time with her loved ones. Her creative spirit extends beyond her writing endeavors, as she finds joy in the art of drawing and immersing herself in the beauty of nature.

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