Susan Buckley, RN, Director, Public Health
Ira Singh, MPH, Deputy Director
Donald I. Baird, MD, Health Officer

Division of Environmental Health


Date Released: 7/14/2005
Contact: Harriet Hill, Registered Environmental Health Specialist
Phone: (707) 445-6215


The Department of Health and Human Services is notifying recreational users of Humboldt County fresh water bodies to avoid contact with water containing significant amounts of algae. In particular, small children and pets should be kept out of such water. Since 2001, there have been 9 dog deaths following contact with water bodies in Humboldt and Mendocino Counties which may have been caused by blue green algae poisoning. Five dogs died after swimming in Big Lagoon, while 4 dogs died after swimming in the South Fork Eel River. Blue-green algae toxin was found in the stomachs of 2 of the dogs that swam in the South Fork Eel River by scientists from the California Animal Health and Food Safety Lab in 2002. No other toxins were detected that could have caused the deaths. There have been no reports of illness or other effects involving humans.

Blue-green algae, which also can be green, brown or red, tends to “bloom” or form large mats when there are low river flows, warm temperatures, and high levels of nutrients such as phosphorus or nitrogen during the summer and fall. When its cells die or are damaged, toxins may be released at levels dangerous to pets and livestock if they drink the water or eat the algae. (Dogs may ingest even more algae when licking their fur after swimming). Human impacts are infrequent because people usually avoid swimming in areas of algae blooms or ingesting algae. However, swimmers or boaters elsewhere have experienced skin irritation, gastrointestinal disorders and allergic respiratory reactions from blue-green algae contact.

The Department of Health and Human Services recommends the following guidelines for recreational users of all freshwater areas:

1. Do not allow pets to swim in or drink river water that is heavily infested with algae.

2. Limit your contact with water where dense mats of algae are visible. Do not wade or swim in this water. Closely supervise young children, who are more at risk due to their small size.

3. Avoid ingesting the river water or algae and handling the algae.

4. Swimmers should shower and pets be rinsed with tap water soon after bathing.

5. Use water-resistant gloves to remove unwanted algae from shorelines.

6. Do not allow your livestock to drink water from water bodies with heavy algal growth.

Pets and other animals that swim in or drink river water are most likely to be affected by blue-green algae toxins. Pet owners should contact their veterinarian if their animal becomes suddenly ill after swimming. Although there have been no reports of human illness in Humboldt County, people could also be affected by the toxins. If swimmers, boaters and other recreational users follow these precautions to avoid direct contact with algae, illness or adverse reactions should be prevented.

The Department does not expect domestic water supplies to be affected unless the water intake is submerged in heavy blue-green algae concentrations. Owners of private water systems should check for algae near water intakes. Algae will cause odor and taste problems in drinking water. All water systems using surface water for domestic use should be first filtered to remove algae cells and then disinfected by a method other than boiling. Disinfection without first filtering the water will kill the blue-green algae, causing it to release its toxins into the drinking water.


In Humboldt County, please contact the Department of Health and Human Services, Division of Environmental Health, at (707) 445-6215 or 1-800-963-9241 for further information on blue-green algae. In Mendocino County, please contact the Mendocino County Health Division of Environmental Health at (707) 463-4466. If you have questions about treatment, call your doctor.

Fact sheets on blue-green algae including information for veterinary workers are available at either county office. For further information concerning animal health, please contact the California Animal Health and Food Safety Lab at (530) 752-6322 or the State Animal Health Branch at (707) 826-1658.


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