County Administrator's Office
For Immediate Release

Recreational water users urged to be cautious about toxic algal mats in local Rivers

Santa Rosa, CA  –  June 22, 2021  –  The State Water Resources Control Board (State Water Board) and Sonoma County Department of Environmental Health Services advise caution for anyone who boats, fishes or swims after harmful algal blooms (HABs) were discovered in multiple Sonoma County rivers. Because children and dogs are most susceptible to serious health impacts, it is recommended that they avoid touching any suspicious-looking algal material found in the water or along river banks.

State Water Board and Sonoma County staff responded to recent sightings of suspected HABs in the Russian River, Salmon Creek and Gualala River. Lab results confirmed that potentially toxic algal mats are growing on the bottom of rivers and may detach and become stranded on banks.

Sonoma County has posted “ Toxic Algae Alert” signs on Salmon Creek, and “ Check For Algae” educational signs on the Russian and Gualala Rivers based upon the statewide guidance. Photos of the HABs are posted on the signs and are available on the Sonoma County Department of Health Services website. Sonoma County and the State Water Board will conduct regular monitoring and provide updates on the California HAB Reports Web Map to inform the community when conditions change.

While harmful algal blooms are caused by algae or cyanobacteria that grow floating in the water, some grow attached to the bottom surface of waterways and can form algal mats.

The State Water Board recommends that people practice healthy water habits when visiting lakes, rivers or streams:

  • Heed all instructions on posted advisories
  • Avoid algae and scum in the water and on the shore
  • Keep an eye on children and pets
  • If you think a harmful algal bloom or toxic algal mats are present, do not let pets and other animals go into or drink the water or eat scum/algal mats on the shore
  • Don’t drink the water or use it for cooking
  • Wash yourself, your family and your pets with clean water after water play
  • If you catch fish, throw away guts and clean fillets with tap water or bottled water before cooking
  • Avoid eating shellfish if you think a harmful algal bloom is present

Get medical treatment immediately if you think any person, pet or livestock has become sick after going in the water. Be sure to alert the medical professional to the possible contact with cyanobacteria. Also, please contact the local county public health department.

To report a bloom, do one of the following:

For more information about HABs, please visit:

California Harmful Algal Blooms Portal: Sonoma County Cyanobacteria website


Contact Information

Paul Gullixson
Communications Manager
County Administrator's Office
County of Sonoma
575 Administration Drive
Suite 104A
Santa Rosa, CA 95403
38.464665, -122.725235