What are Cyanobacteria?
Cyanobacteria or Bluegreen Algae are bacteria capable of photosynthesis - creating their own energy from the sun. These organisms occur naturally in surface water such as lakes, ponds, rivers and streams.When conditions are right - excess nutrients, warm temperatures, and sunshine, they can rapidly form blooms of Harmful Algal Blooms characterized by the presence of toxins produced by the bacteria.


What are the health effects of the toxins?
The toxins produced by the bacteria (cyanotoxin) can cause skin irritation such as rashes, hives, swelling or blisters. Consuming raw water that contains these toxins can cause liver damage. This may occur during recreational activities such as swimming. Due to their smaller size and tendency to drink lake water, pets can suffer more detrimental effects including death. Children too should be cautioned not to drink water out of the lake.

Click here for more information on Health Effects and Precautions


How will I be alerted about a bloom?
Watch for public information releases from the County, monitor the Water Resources Facebook page and pay attention to Nixle announcements. If a toxic bloom is occurring the County or City will post signs stating whether there is a water contact WARNING or a water contact DANGER.  Sample images of the signs are shown below.


Signs Combined

Has there been a bloom in my area?

During the 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 and the Elem Indian Colony.  To find out if a bloom is occurring, visit The Clear Lake Cyanotoxin page by clicking here.

Where can I find historical occurrences of bloom and/or report a bloom?

Information on recent occurrences in Lake County, and other locations in the state can be found on the California Harmful Algal Bloom (HABs) Portal located by clicking here.  The Portal is an informational resource for the public and also functions as a tool to support coordination with statewide partners to address HABs. The content is developed by the CA Cyanobacteria and HAB Network and participating state agencies.


Current Cyanobacteria concentrations map - Big Valley Cyanotoxins page
California Water Board HAB ID Factsheet

Lake County Public Health Office
Environmental Health Bluegreen Algae Page
Informative Cyanobacteria Brochure (Contact us for hard copies)
Informative Cyanobacteria Brochure(Spanish) (Contact us for hard copies)