Clear Lake is a natural freshwater lake in Lake County in the U.S. state of California, north of Napa County and San Francisco. It is the largest natural freshwater lake wholly within the state, with of surface area. (Lake Tahoe is partially in Nevada.) It has an age of nearly 500,000 years. It is the latest lake to occupy a site with a history of lakes stretching back at least 2,500,000 years.
Clear Lake supports large populations of largemouth bass, crappie, bluegill, carp and catfish. Two-thirds of the fish caught in Clear Lake are largemouth bass, with a record of . In addition to fish, there is abundant wildlife within the Clear Lake basin. There are year-round populations of ducks, pelicans, grebes, blue herons, egrets, osprey, and bald eagles, and the basin supports sizable populations of deer, bear, mountain lion, raccoon and other animals.
The expansive, semi-warm water of Clear Lake makes it popular for watersports, such as swimming, water skiing, wakeboarding, sailing, boat races, and jet skiing.
Nomenclature Hok-has-ha, Ka-ba-tin, and Lupiyoma are the original names given to Clear Lake by the indigenous people of the region, the Pomo, Lake Miwok and Wappo. In the early 19th century, European American settlers referred to the lake as "Big Lake" or "Laguna", before finally adopting Clear Lake by the mid-19th century.
Hydrology Clear Lake is by at its widest point, with a surface area of and a capacity. Average depth is , maximum is , lake elevation is , and average water temperature is in winter and in summer.
The Clear Lake Watershed is contained within the Upper Cache Creek USGS hydrologic unit, an area that encompasses roughly . The drainage basin is ( including the lake), which is large compared to the lake's . The surface area of the lake is divided into three arms: the Upper Arm, the Oaks Arm and the Lower Arm. Cache Creek, the only outlet for the lake, originates from the Lower Arm. Cache Creek has two major tributaries: North Fork Cache Creek and Bear Creek. The Upper Arm is the largest of the three arms and receives 75% of drainage from the watershed. Rodman Slough, contained within the Upper Arm, receives drainage to its marsh from Scotts Creek and Middle Creek, the largest tributaries to Clear Lake as well as Kelsey Creek, which enters from Big Valley. Erosion and sedimentation are key environmental concerns in the Clear Lake region. Seventy percent of the terrain has very shallow topsoil, which saturates after a rainfall of , after which runoff flows quickly into the lake. The maximum flow from the lake is determined by the narrow canyon of Cache Creek, not by the dam. The combination of rapid inflow and slow outflow results in frequent flooding of low-elevation areas such as downtown Clearlake and Lakeport.Page 21In the past forty-one years, federal disasters due to flooding were declared six times in the City of Lakeport during 1983, 1986, 1995 (twice), 1997, and 1998.
Geology Clear Lake is believed to be one of the oldest lakes in North America.The lake sits on a huge block of rock which slowly tilts northward at the same rate as the lake fills in with sediment, thus keeping the water at roughly the same depth. Core samples of the lake's sediments, taken by U.S. Geological Survey geologists in 1973 and 1980, indicate that the lake is at least 480,000 years old.
At one time Clear Lake was even bigger than it is now, and included the Blue Lakes (to the northwest of Clear Lake). Volcanic eruptions and subsequent landslides changed the landscape dramatically, forever separating Clear Lake from the Blue Lakes and from its former westward drainage into the Russian River.
Clear Lake lies within the Clear Lake Volcanic Field, as designated by the United States Geological Survey. The volcanic field contains The Geysers, a steam field which powers a network of the world's most productive geothermal power plants. There are numerous small faults present in the south end of the lake as well as many volcanoes, ranging in age from 10,000 to 2.1 million years, the largest being Mount Konocti, sitting at the middle of the lake's south shore. There have been no eruptions from the Clear Lake Volcanic Field for thousands of years, but there are indicators currently being monitored that suggest there is the potential for future eruptions. These indicators include volcanic-type earthquakes, hot spring activity and seepage of volcanic gas.
Weather It is not uncommon for temperatures in the summer to rise into the triple digits, or fall below freezing in the winter. Occasional summer thunderstorms occur but are not common. Snow can fall to lake level but accumulation is rare. Snow on the surrounding mountains is common.
The average high temperature is in summer, and the average low is in winter. Normally, July is the hottest month and December the coldest. December and January are the wettest months, with an average of of rain per month, respectively.
Recreation With over of shoreline, Clear Lake is a popular spot for water-sports enthusiasts. According to the California Water Board, Clear Lake sees 15,000 recreational boaters per year. There are 11 free boat launch ramps around the lake that are open to the public. Individuals may rent boats and personal watercraft from many businesses around the lake.
Clear Lake is sometimes called the "Bass Capital of the West." Largemouth bass, which are farmed and planted in the lake by California Department of Fish and Wildlife, crappie, catfish, bluegill, and rainbow trout can be found in the county's lakes. Fishing boats can be rented, and many stores and facilities around the lake specialize in fishing equipment. Numerous fishing tournaments and derbies are held throughout the year. In 2016, Clear Lake was ranked by Bassmaster Magazine as the #3 best bass lake in the United States and the #1 best bass lake on the West Coast.
All boaters entering Lake County are warned that Dreissenid mussels, also known as quagga and zebra mussels, are a great threat to Clear Lake. By law, boats are required to be inspected before launching, and must have a Lake County Quagga/Zebra (QZ) Sticker on the watercraft. Shops in the vicinity carry out the inspection. At every entry to Lake County, signs warn boaters not to spread hydrilla in the county's bodies of water. Extensive management efforts have controlled the presence of hydrilla in Clear Lake, although it may return at any time.
The lake is also the site of an annual "splash-in", the "oldest and largest seaplane gathering in the Western United States".
The California Office of Environmental Health Hazard Assessment released an advisory statement regarding eating fish caught from the lake, based on the mercury level.
Wildlife and vegetation The Clear Lake basin attracts large quantities of waterfowl, including mallards, western grebe, coots, various species of geese, ospreys, plovers, mergansers and many others. Wild turkeys, blacktail deer, gray squirrels, ground squirrels, skunks, river otter, raccoon, mink, and muskrat. There have been occasional sightings of mountain lion and ringtail. Opossums, red-tailed hawks, turkey vultures, and other species are also common. The endangered northern spotted owl is seen occasionally. Common reptiles and amphibians include the northwestern pond turtle, California king snake, Pacific gopher snake, garter snakes, northern pacific rattlesnake, common bullfrog and the rare California giant salamander among many others. Much of the shoreline is developed, but parks, reserves, miles of open water and private land also exist allowing many opportunities for observing and enjoying nature. The county also hosts a growing population of the rare tule elk, recently reintroduced after being locally hunted to extinction one hundred years before. A large colony of bald eagles is found in the Cache Creek canyon.
In addition to the native Clear Lake hitch (called chi by the native Pomo), the lake hosts channel catfish, white catfish, brown bullhead, crappie (both black and white species), and other native fish species, as well as Florida strain largemouth bass and carp placed by the Department of Fish and Wildlife for sporting purposes. Along the shoreline and creeks, there are aquatic growths of tule, cattail, willow, cottonwood, box elder, and many other types of riparian plant life.
The streams feeding Clear lake contain Sacramento pikeminnow, California roach, and rainbow trout. Pacific lamprey are present in at least one stream, Kelsey Creek. Prior to the construction of a dam on the outlet of Clear Lake, both steelhead and Pacific lamprey ascended Cache creek to spawn in Clear Lake's tributaries. As of March 2024, farming operations along the Big Valley Groundwater Basin watershed have been ordered to report of their water use by the California State Water Resources Control Board in order to study the effect of groundwater pumping and water diversions on the Clear Lake hitch spawning and migration.
Clear Lake is well known among entomologists for the Clear Lake gnat (Chaoborus astictopus) and historical control efforts. This species of "phantom midge" (so called because the larvae are transparent and very difficult to see) measures less than long and resembles a tiny mosquito, but is non-biting. Clear Lake gnat hatches start anytime from March through June, depending on weather. Before pesticide use began in the 1940s, the gnat was so abundant around the lake in the summer that large piles of dead gnats appeared beneath streetlights, looking like dirty snow. The gnat swarms were so thick that people driving along the edge of the lake reported stopping every to clean the insects off the windshields and headlights of their cars so they could see, and pedestrians tied kerchiefs over their faces to avoid inhaling the gnats.
The rugged coastal mountains surrounding Clear Lake are covered with thick stands of oak-madrone forest, manzanita, sage shrubs, chaparral, and grasses. Most common trees include blue oak, valley oak, interior live oak, Pacific madrone, California scrub oak, plus very occasional coast redwoods and tanoak. Large stands of western white pine may be seen in the higher elevations. The heavy forestation and ruggedness of this part of California has helped prevent wholesale real estate development or farming. On the northeast slope of Mount Konocti is a heavily forested area known locally as the "Black Forest" because it never gets direct sunshine. This area has some Douglas fir in very heavy stands.
History
Archaeologists believe that the Clear Lake basin has been occupied by Native Americans for at least 11,000 years. (See: Post Pattern.) Evidence of this has been found at nearby Borax Lake and on Rattlesnake Island in the lake's south arm. Abundant fish, game and waterbirds made Clear Lake an oasis in the otherwise harsh conditions of Northern California's mountains. The native Clear Lake Hitch (Lavinia exilicauda) was once so abundant that millions of hitch clogged the lake's feeder streams in dry months. When the Spanish missionaries came to California, they found that thousands of Native Americans lived in the Clear Lake Basin, primarily Pomo, Yuki, and Wappo with some Lake Miwok.
European settlers arrived starting around 1845. Frequently they abused and exploited the native Pomo people. A number of Pomo were enslaved and abused by settlers, notably Andrew Kelsey (whose name is attached to the town of Kelseyville) and Charles Stone. The Pomo eventually revolted and killed Kelsey and Stone in 1849. The following year, a United States Army contingent under Lieutenant Nathaniel Lyon cornered as many as 200 Pomo on an island in Clear Lake and slaughtered most of them—including scores of women and children. The historical marker for the Bloody Island massacre is on Highway 20 between Upper Lake and the Robinson Rancheria. The Pomo were later forced to live in small rancherias set aside by the federal government.