Blue-Green Algae (Cyanobacteria)

Algae, including blue-green algae (aka cyanobacteria), is a normal inhabitant of many water environments. Certain conditions, such as high temperatures and elevated nutrient concentrations allow algae to grow more rapidly than usual creating mats or blooms. Most algae is harmless; however, some species of blue-green algae can produce toxins which create health effects for humans and animals.

The Department of Health Services and the North Coast Regional Water Quality Control Board are in the second phase of our pilot blue-green algae monitoring program in which we test water samples and based on those results provide guidance regarding recreational use of the Russian River. Water samples collected on September 17th showed low levels of blue-green algae toxins present in certain areas of the river.

In accordance with state guidance, and consistent with our actions in prior years, the level of toxin present is enough to trigger the posting of yellow “Caution” signs in both English and Spanish at all major beaches along the River. These signs were posted on September 19, 2018.

“Caution” is the lowest of three levels of state recommended advisory signage (“Caution”, ”Warning” and “Danger”). After two weeks of no detection of toxins signs were removed September 12 from public beaches in accordance with state guidelines. This week toxins were detected and Caution signs will be posted, as per State guidelines, warning the public that potentially harmful algae may be present and care should be taken to keep children and pets away from algae, and prevent them from drinking river water.

Signs will include these recommendations:

  • Stay away from algae in the water.
  • Keep children away from algae in the water, on the shore and in isolated side pools.
  • Do not drink river water or use for cooking.
  • Do not let pets drink the water, or eat scum on the shoreline.
  • For fish caught here, throw away guts and clean fillets with tap water or bottled water before cooking.
  • Rinse off thoroughly with clean water after river play, particularly children and pets.

Download 2018 test results - all locations

Test Results from Previous Year

State Trigger Levels

CautionAny detected1 μg/L0.8 μg/L
Warning20 μg/L4 μg/L6 μg/L
Danger90 μg/L17 μg/L20 μg/L

Source: State Water Resources Control Board

All levels are in μg/L.

Related Links

California Harmful Algal Blooms (HABs) Portal
Source:California Water Quality Monitoring Council

Resources for Mitigating Harmful Algal Blooms (HABs)
Source:California Water Quality Monitoring Council

Are Harmful Algal Blooms Affecting Our Waters?
Source: State Water Resources Control Board

Algal Blooms
Source: California Department of Public Health.

California Cyanobacteria and Harmful Algal Bloom (CCHAB) Network
Source: California Water Quality Monitoring Council

Harmful Algal Bloom (HAB)-Associated Illness
Source: Centers for Disease Control and Prevention

Contact Information

Public Health Division
County of Sonoma
Business Hours
Monday – Friday
8:00 AM – 4:00 PM
Office Location
625 5th Street
Santa Rosa, CA 95404
38.44178, -122.7158781

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