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

Division of Environmental Health


Date Released: 6/22/2007
Contact: Harriet Hill, Registered Environmental Health Specialist, Environmental Health Division
Phone: (707) 445-6215

The Humboldt County Department of Health and Human Services is notifying recreational users of the South Fork Eel River, Big Lagoon, and other fresh water bodies to take precautions to avoid contact with blue green algae. 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. At least 2 of these dogs were found to have ingested blue green algae toxin. Over the past few years, high levels of the blue green algae Microcystis aeruginosa and its toxin have been detected in Copco and Irongate Reservoirs on the Klamath River in northern Siskiyou County. Much smaller amounts of these algae were present downstream in the Klamath River. There have been no reports of illness or other effects involving humans.

Blue-green algae can look like green, blue-green, white or brown scum, foam or mats floating on the water. Blue green algae “blooms” or large build-ups of algae can be triggered by low river flows, warm water, and high nutrient levels in the summer and fall. When algae cells die or are damaged, toxins may be released at levels dangerous to livestock, pets and humans if they drink the water or ingest the algae. Dogs may eat algae when licking their fur after swimming. Human impacts are infrequent because people usually do not drink open surface water, or swim in areas with lots of algae. However, swimmers or boaters elsewhere have experienced skin irritation, gastrointestinal disorders and allergic respiratory reactions from blue green algae contact. Children are most likely to accidentally ingest algae and water. Also, their small body weight means their exposures to blue green algae will be higher than adults, given the same amount of water intake

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

1. Keep pets and livestock from swimming in or drinking water containing algal scums or mats.
2. People should avoid wading and swimming in water containing algal scums, mats or blooms.
3. If no algal scums or mats are visible, you should still carefully watch young children and warn them not to swallow any water.
4. Fish should be consumed only after removing the guts and liver and rinsing fillets in tap water.
5. Never drink or cook with water from rivers, streams or lakes. In addition to blue green algae, open surface waters can contain harmful bacteria and parasites.

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

Algal blooms can be stimulated during warm weather by high concentrations of nutrients in the water. Human activities can have a big effect on nutrient flows into rivers, streams or lakes. Two important nutrients required by algae are phosphorous and nitrogen. These are found in animal waste, human waste (sewage), and fertilizers. Excessive amounts of phosphorus and nitrogen may lead to “nutrient loading” and eventually to an algal bloom. People can take the following measures to reduce nutrient loading in our waters:

1. Be extremely cautious with the application of fertilizers and pesticides on your lawn or garden. Don’t over-water, over-fertilize, or use more than the recommended amount of pesticides.
2. Plant or maintain native plants around banks and shorelines. Native wetland and streamside plants help filter water and don’t require fertilizers or pesticides to stay healthy.
3. Operate and maintain your septic system properly. Poorly operated or damaged septic systems can increase nutrient loading into nearby water. Have your system pumped and inspected every 3-4 years
4. Prevent surface water runoff from agricultural and livestock areas. Do not allow livestock to wallow in rivers, streams or lakes. Don’t feed waterfowl.
5. Prevent erosion around construction and logging operations. Erosion can carry nutrient-rich soil into nearby water bodies.


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 become most intense after 2-3 days, after which they 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.

For additional information on blue green algae including measures to protect drinking water systems, see the California Department of Health Services website:


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