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Cyanobacteria Bloom in Clear Lake July 20th

Caution Urged for Water Contact at Elem Indian Shoreline (ELEM01), Redbud Park (RED01), and Keeling Park (KPO1)
Danger Urged in Water Contact at Clearlake Oaks (CLOAKS01) and in Richmond Park (RP)


Lake County– Public Health is urging boaters and recreational users to avoid direct contact with or use of waters containing blue-green algae (cyanobacteria) in Richmond Park and Clearlake Oaks in Lake County.

The recommendation is based on the potential health risks from the algae, which is currently blooming in all three arms of the Lake (Upper arm, Oaks Arm, and Lower Arm).

Relevance of results to the Office of Environmental Health Hazard Assessment (OEHHA) trigger levels or action levels

Bloom conditions can change rapidly and wind and waves may move or concentrate the bloom into different regions of Clear Lake.  Lake-wide sampling on 7/17 indicated that blooms were present in several locations on Clear Lake.  The CLOAKS01 site lab result showed a level of 480 µg/L, which is at the danger level. The Richmond Park site lab result showed a level of 25 µg/L, which is also at the Danger level. The ELEM01 site showed a level of 4.9 µg/L, the RED01 showed a lab result of 4.1 µg/L, and the KP01 site showed a lab result of 4 µg/L; all of these results are at the Caution level.

The Clearlake Oaks location is close to a drinking water supply.   Drinking water at CLOAKS01 was tested last on July 10th and was below the Environmental Protection Agency (EPA) recommended guideline of 0.3 µg/L and was safe to drink.  Sampling of drinking water at the CLOAKS01 site will next occur on Monday July 23rd.  The Richmond Park location is close to a drinking water supply. Sampling of drinking water at the RP site will occur on Monday, July 23rd.

Blue-green algae can pose health risks, particularly to children and pets. We urge people to choose safe activities when visiting the Oaks arm and parts of the lower arm of Clear Lake and wherever blooms are visible.  It is strongly recommended that people and their pets avoid contact with water, and avoid swallowing lake water in an algae bloom area.



Clearlake Oaks (CLOAKS01) at Beach

Algae at Clearlake Oaks Beach July 17, 2018

Clearlake Oaks Algae July 17, 2018

Richmond Park (RP)

Richmond Park Algae July 17, 2018

See map below for Red arrow (Danger) and Orange arrow (Warning), signs should be posted.
Algae Map July 20 2018


Current Results - 2018 Sampling Results/Locations

Green Markers - Below California trigger levels
Blue Markers - Regular sites not sampled during this last sampling event
Yellow Markers - Caution trigger level
Orange Markers - Warning trigger level
Red Marker - Danger trigger level

The algae bloom can appear as cut grass in the water or blue-green, white or brown foam, scum or mats that can float on the water’s surface and accumulate along the shoreline and boat ramp area.

Recreational exposure to toxic blue-green algae can cause eye irritation, allergic skin rash, mouth ulcers, vomiting, diarrhea, and cold and flu-like symptoms.  Pets can be especially susceptible because they tend to drink while in the water and lick their fur after.

What is Cyanobacteria?  
Cyanobacteria (also known as blue-green algae) are common and natural to our waters and found throughout California. Cyanobacteria thrive in nutrient-rich water and can multiply rapidly to form blooms and scums, particularly during the warm days of summer and early fall.

A blue-green algae bloom:
Resembles thick “pea soup”.
Looks like “spilled paint” on the water’s surface.
Creates a thick mat of foam along the shoreline.
Is generally green or blue-green in color, although it can be brown, purple or white.
Is made up of small specks or blobs floating at or just below the water surface.

A blue-green algae bloom is NOT:
Stringy, made up of long bright grass-green strands that feel either slimy or cottony. This is harmless green algae.
Mustard yellow in color. This probably is pollen.

What are the health effects?
General health effects caused by exposure to blue-green algae:
Rashes or other skin irritations.
Allergy-like reactions, runny nose or sore throat.

Some blue-green algae naturally produce toxins or poisons. When these toxins are ingested in large amounts they can cause:
Sharp, severe stomach problems like diarrhea and vomiting.
Liver damage that may take hours or days to show up in people or animals.
Numb limbs, tingling finger and toes or dizziness.

Possible health effects of animal exposure to a toxic bloom:
•   Weakness, staggering
•   Difficulty breathing
•   Convulsions
•   Vomiting or diarrhea

Signs of a toxic bloom may include: a large number of dead fish, waterfowl or other animals, or sudden, unexplained sickness or death of a cat or dog that has been exposed. It is not possible to tell if cyanobacteria are toxic by looking at them.

There is ongoing research on potential health effects of exposure to the toxins produced by some species of cyanobacteria. The California Department of Public Health evaluates any new findings and makes updates to guidance materials as necessary.

How might I be exposed?
Examples of ways in which one can be exposed to blue-green algae:
Boating, jet-skiing, swimming and other recreational activities near or through blooms.
Drinking untreated water with toxins present. Children and pets have a higher risk of exposure to blue-green algae because they are more likely to play near the shoreline where blooms are often thickest and because they are more likely to ingest this water. Public water systems on Lake Champlain work with state partners to monitor blooms that could impact the quality of drinking water.

How can I protect myself?
Avoid contact with surface scums of blue-green algae or with water that appears deeply green, blue or white in color.
Follow all instructions on posted signs.

Bloom reporting and information
Call: 1 (916) 341-5357
Call toll free: 1 (844) 729-6466
Only laboratory tests of water samples can confirm whether a bloom is toxic.

The Statewide Guidance on Cyanobacteria and Harmful Algal Blooms recommends the following for waters impacted by blue-green algae:
Take care that pets and livestock do not drink the water, swim through algae, scums or mats, or lick their fur after going in the water.  Rinse pets in clean water to remove algae from fur.
Avoid wading, swimming, jet or water skiing in water containing algae blooms, scums or mats.
Do not drink, cook or wash dishes with untreated surface water from these areas under any circumstances; common water purification techniques such as camping filters, tablets and boiling do not remove toxins.
People should not eat mussels or other bivalves collected from these areas.  Limit or avoid eating fish from these areas; if fish are consumed, remove the guts and liver, and rinse filets in clean drinking water.
Get medical treatment immediately if you think that you, your pet, or livestock might have been poisoned by blue-green algae toxins.  Be sure to alert the medical professional to the possible contact with blue-green algae.  Also, make sure to contact the local county public health department at (707) 263 - 1090.

For more information, please visit:

Big Valley Rancheria EPA – for updated toxin levels

Elem Indian Colony EPA

California Harmful Algal Blooms Portal:

California Cyanobacteria and Harmful Algal Bloom (CCHAB) Network:

California Surface Water Ambient Monitoring Program Freshwater HAB webpage:

California Department of Public Health:

CA Office of Environmental Health Hazard Assessment: Information on Microcystin

US Environmental Protection Agency: CyanoHAB website 

US Environmental Protection Agency: Anatoxin-a report 

Lake County Website


Cyanobacteria film on top of water

Recreating in Lakes & Streams

With warm weather in the forecast and recreational water sports gearing up, health and water resource officials across the state are reminding the public to be mindful of cyanobacteria (also known as blue-green algae).

More info