Notice of Reorganization

Fact Sheet:  Staying Safe When Cyanobacteria and Harmful Algal Blooms are Present

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). These are microscopic organisms that naturally occur in all freshwater and marine aquatic ecosystems.

Usually, cyanotoxin concentrations are low, and not harmful to animals and humans. Sometimes, when conditions are favorable (high nutrients and warm weather), these organisms can rapidly grow, forming visible colonies or “blooms.”
Cyanobacteria, and even some algae, produce toxins that reach hazardous levels when blooms occur. These are called cyanotoxins and are classified as Harmful Algal Blooms (HABs). Blue-green algae is not to be confused with green algae, which is beneficial, non-toxic, and always present in Clear Lake. Water testing is the best way to identify the type of algae that is in the lake at a specific time. During warm seasons, water quality testing is conducted about every two weeks at over 20 locations throughout Clear Lake. This testing is
provided by the Big Valley Band of Pomo Indians.

To find out if a bloom is occurring, visit the Clear Lake Cyanotoxin Monitoring webpage. This page will have the most current cyanotoxin lab results for the monitoring locations on the shoreline and interior of Clear Lake:

The public can look for permanent informational signs throughout the county and cities, at all public parks and public access points that coincide with the water testing locations. Please see the map, below, showing water testing locations.

We are already seeing Caution levels around the lake this season. Additional signs are posted when cyanotoxins reach Caution, Warning, or Danger levels. These signs are brightly colored, and affixed below the permanent informational signs in order to provide the public specific guidance on which activities are safe to continue.

The permanent signs are the culmination of a collaborative communication effort between multiple partners:  The County of Lake, Big Valley Band of Pomo Indians, Elem Indian Colony, the City of Lakeport, and the City of Clearlake. The signs include a QR code which can be scanned by a smart phone and will take you the Big Valley Rancheria Clear Lake Cyanotoxin Monitoring website.

If you would like to post a sign at your beach or ramp, please contact Water Resources at (707) 263-2344. If you see, or think you see, a cyanobacteria bloom, please contact Water Resources at (707) 263-2344, Environmental Health at (707) 263-1164, or Public Health at (707) 263-1090. Anyone can report a bloom and/or receive additional information at the California Harmful Algal Blooms Portal:

The below map shows the results from the last testing preformed on May 17, 2021. The six yellow pins are caution levels, the two orange are warning and the one red is danger level.
Cyanobacteria Map
Cyanobacteria SignThis picture shows a permanent sign installed at Lakeside County Park in Kelseyville.

The Statewide Guidance on Cyanobacteria and Harmful
Algal Blooms recommends the following for waters
impacted by harmful cyanobacteria:
  • Keep pets and other animals out of the HAB-affected water. Do not allow them to drink the water or eat algal material (scum) on shore. If they do get in the water, do not let them drink the water, swim through algal material, scums or mats, or lick their fur after going in. Rinse pets in clean water to remove algal material and potential toxins from fur. 
  • Do not drink, cook or wash dishes with untreated surface water from HAB-affected 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 HAB-affected 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 has gotten sick after going in the water. Be sure to alert the medical professional to the possible contact with blue-green algae. Also, make sure to contact the County Health Services Department’s Public Health Division (707-263-1090).
Remember to always practice healthy water habits:
  • Heed all instruction on posted advisory signs.
  • Avoid body contact with water that looks discolored, like spilled paint, or has a green/blue surface scum, mats, or film, or is emitting a foul odor, or if Caution, Warning, or Danger signs are posted.
  • Keep an eye on children and dogs, ensuring that they do not approach areas with water has the above appearance or foul odor, or if Caution, Warning, or Danger signs are posted.
  • Do not drink untreated lake or river water. Common water purification techniques such as camping filters, tablets and boiling do not remove cyanotoxins.
  • Do not cook or wash dishes with lake or river water.
  • Wash yourself, your family, and your pets with clean water after lake or river play.
  • Consume fish only after the guts and liver have been removed and rinse filets.
For current monitoring data, please visit the Big Valley Band of Pomo Indians’ cyanotoxin monitoring website:

For more information, please visit:
County of Lake Cyanobacteria brochure:

County of Lake Cynobaceria brochure (in Spanish):
Physician Reference Sheet:
Domestic Animals and HABs:
County of Lake Cyanobacteria Webpage:
California Cyanobacteria and Harmful Algal Bloom (CCHAB) Network:
California Surface Water Ambient Monitoring Program Freshwater HAB webpage:
Centers for Disease Control and Prevention (CDC):
U.S. Environmental Protection Agency: CyanoHAB website