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

Division of Environmental Health


Date Released: 7/15/2004
Subject: Blue Green Algae and Swimmer's Itch
Contact: Kevin Metcalfe, Supervisor, Environmental Health Division
Phone: (707) 445-6215


The Department of Health and Human Services is notifying recreational users of the South Fork Eel River and other fresh water bodies to take precautions to avoid contact with blue green algae. In 2002 three dog deaths occurred after the animals swam in areas of stagnant water with significant growths of blue green algae. At least two of these deaths were most likely caused by the ingestion of blue green algal toxins.

The Mendocino County Environmental Health Division, and California Animal Health and Food Safety Lab found blue green algae and their associated toxins in South Fork Eel River water samples, and in the stomach contents of two of the dead animals. No other toxins were found that could have caused the deaths. There have been no reports of illness or other effects involving humans.

Blue green algae “blooms” or large build-ups of algae can be triggered by low river flows and high nutrient levels in the summer and fall. When algae 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 algae when licking their fur after swimming). Human impacts are infrequent because people usually avoid ingesting algae or swimming in areas of algae blooms. 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 algae blooms are visible, particularly dense mats of algae. Do not wade or swim in this water. Closely supervise young children, as they are more at risk due to their small body size.
3. Do not drink, eat or handle the algae and avoid ingesting the river water.
4. Swimmers should shower and pets be rinsed with tap water immediately after bathing.
5. Use water-resistant gloves to remove unwanted algae from shorelines.
6. Ranchers should not allow livestock to drink water from contaminated rivers or streams.

Although there have been no reports of human illness in Humboldt County, people could be affected by the toxins. Pets and other animals that swim in or drink river water are most likely to be affected by blue green algae toxins. However, following the above precautions to avoid direct contact with algae should prevent an illness or any adverse reaction.

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.


Swimmer’s Itch (schistosome dermatitis) is a common hazard for bathers during the warm summer months in some of the lakes and slow moving streams in Humboldt County.

Swimmer’s Itch occurs when a small parasite burrows under the skin of bathers. The parasite cannot survive in humans and does not infect us. The symptoms, which include tingling skin, moderate to severe itching, and small bumps or eruptions, usually reach maximum intensity after 2-3 days, after which the symptoms subside on their own. There are no long-term effects from Swimmer’s Itch. Sufferers may get relief from oral antihistamines or topical salves or ointments.

To avoid Swimmer’s Itch, swimmers in suspect waters should leave the water every ten minutes and vigorously towel dry. This will help remove the parasites before they burrow into the skin.


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 or swimmer’s itch. 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 State Animal Health Branch at (707) 826-1658.


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