Clear Lake is Unique

Clear Lake is the largest, natural freshwater lake in California with 68 square miles of surface area. Clear Lake is very productive and scenic, a lush paradise for fish and wildlife. The high productivity of the Clear Lake Basin attracted Native Americans early in their settlement of North America. Archeological evidence indicates human habitation around Clear Lake for the last 12,000 years.

Known as the Bass Capital of the West, Clear Lake supports large populations of bass, crappie, bluegill, carp and catfish. Two-thirds of the fish caught in Clear Lake are largemouth bass, with a record of 17.52 pounds. Bass fishing and fishing tournaments held on Clear Lake bring fishermen and women from all over California and other States.

In addition to fish, there is abundant wildlife within the Basin. There are year-round populations of ducks, pelicans, grebes, blue herons, egrets, osprey, and bald eagles. The Basin also supports abundant populations of deer, bear, mountain lion, raccoon and other animals.

The expansive warm, water of Clear Lake makes it popular for watersports, such as swimming, water skiing, wakeboarding, sailing, boat races, and jet skiing. With its scenic beauty, clean air and abundant wildlife, Clear Lake is an excellent place to slow down, enjoy nature study, photography or just plain loafing.

Algae & Cyanobacteria (Blue-Green Algae)

Along with Clear Lake's high productivity, “algae" in the lake can create a situation which can be perceived as a problem to humans.  “Algae” in Clear Lake consist of two major groups, green algae and cyanobacteria, frequently referred to as blue-green algae.  Green algae are tiny water plants that float within the water column. Green algae are an important part of the food chain and lead to the high fish and wildlife populations in and around Clear Lake.  Cyanobacteria are actually photosynthetic bacteria and not true algae at all.  Cyanobacteria can control their buoyancy and cycle normally between the bottom and the surface, floating up and sinking down.  Cyanobacteria can dominate the lake ecosystem by remaining at the surface and reducing the light available to green algae.  During the day, both green algae and cyanobacteria generate oxygen within the lake; at night they consume oxygen. 

Algae and cyanobacteria in Clear Lake are part of the natural food chain and keep the lake fertile and healthy. Because of the lake's relative shallowness and warm summer temperatures, the algae serve another important purpose. They keep the sun's rays from reaching the bottom, thus reducing the growth of water plants which would otherwise choke off the lake. The improved springtime clarity since 1990 has increased the number of water plants in the lake providing important shelter for fish, however, it does make it difficult to swim or navigate boats in areas with heavy growth.

Cyanobacteria, however, can be a problem. From more than 130 species of algae and cyanobacteria identified in Clear Lake, five species of cyanobacteria can create problems under certain conditions. These problem cyanobacteria typically "bloom" three times a year, in spring, summer and late summer. Each bloom is dominated by a different species of cyanobacteria that thrives in the conditions at that time of year.  The intensity of the blooms vary from year to year, and are unpredictable. The problem occurs when cyanobacteria blooms are trapped at the surface and die. When this occurs, unsightly slicks and odors can be produced.  Some cyanobacteria may produce cyanotoxins that can pose a range of health risks to people and animals.

The most effective method of keeping the cyanobacteria from becoming a nuisance is to keep them alive and in a normal cycle. This may be done by agitating the water surface to break up the trapped cyanobacteria, letting it sink. Boat traffic and spraying the trapped cyanobacteria with water have proven effective in breaking up the trapped surface algae.

What do I need to know about interacting with cyanobacteria?

Skin irritation or rash is a commonly reported health effect. Other symptoms range from gastrointestinal discomfort to neurological effects. The most severe reactions occur when large amounts of water are swallowed. Because dogs are smaller bodied than people and will tend to drink water when swimming or lick their fur, it is advisable to keep dogs out of the water during a cyanobacteria bloom.
If you decide to go in the water, avoid ingesting the water and rinse off with tap water soon after exiting. Use your own best judgment – When in Doubt, Stay Out!

This Fact Sheet from USEPA provides more information.

Common Questions
Is the lake eutrophying or dying?

The lake is definitely not dying. It is healthy and very much alive. A lake is eutrophic when it is productive in the same way a grassy field is more productive than a desert. Studies indicate that Clear Lake is eutrophic now and has been eutrophic for more than 10,000 years. Cyanobacteria populations increased significantly in the 1930’s due to the impacts of development in the watershed.  With implementation of watershed protection measures since the 1970’s, such as erosion control, gravel mining regulation, return of riparian corridors along streams, improved agricultural practices, etc., some of the development impacts have been reversed.  Additional watershed protection and restoration measures are required to further mitigate development impacts.

Are dead fish around the lake due to a lack of oxygen in the water?

Although oxygen levels in land-locked areas, such as channels, can get dangerously low for aquatic life, oxygen in the open surface waters of Clear Lake is always high enough to sustain fish. Near the lake bottom, oxygen levels may be lowered, but this area is usually avoided by fish. Natural conditions of old age, disease and rapid temperature changes are more likely causes of dead fish in Clear Lake.

Is the lake water safe to drink?

Disease-causing organisms are present in nearly all surface waters, even crystal clear mountain streams. As with all natural surface waters, drinking water directly from the lake should be avoided. Lake water must be properly treated to be safe to drink. All lake water treated by the public water supplies around the lake is safe to drink. 

Is it safe to eat fish caught in the lake?

It is not clear whether cyanotoxins affect the edibility of fish, as they may accumulate in the organs.  Eating of fish organs should be avoided.

Due to elevated mercury levels in some of Clear Lake's fish, the advisory from the California Office of Environmental Health Hazard Assessment limiting the number of fish consumed should be heeded. Mercury occurs naturally in Clear Lake, although levels have been elevated due to historic mercury mining at Sulphur Bank. The U.S. Environmental Protection Agency has begun remedial steps including the reinforcement and stabilization of the shoreline and drainage improvements to reduce the input of mercury to the lake. Additional remediation measures are being investigated.

Reducing Cyanobacteria

The County of Lake has supported research and several projects to reduce the growth of cyanobacteria in Clear Lake. Working in cooperation with the State Department of Water Resources and the University of California, Lake County officials completed studies that have shown there is an over-abundance of nutrients (food for the algae and cyanobacteria) within the lake. Because the lake is so large, spraying cyanobacteria to reduce nuisance conditions is not a practical long term solution. Reduction of lake nutrient levels is anticipated to reduce the quantities of nuisance cyanobacteria.

Nutrients come from erosion and other sources within the watershed, the land which drains into Clear Lake. A key to improving the water quality in the lake is to manage the entire watershed. Measures to reduce the nutrient loading to clear Lake have been implemented since the 1970’s.  Continued implementation of erosion control, creek and wetland protection and restoration, and improved land management practices are necessary to improve the water quality of Clear Lake by reducing the nutrient load to Clear Lake.

For technical information on Clear Lake, please contact the Lake County Water Resources Department, at (707) 263-2344 or write 255 North Forbes Street, Lakeport, CA 95453.

For recreation information around Clear Lake, please contact the Lake County Marketing Program at (800) 525-3743, (707) 274-5652, or write 255 North Forbes Street, Lakeport, CA 95453.