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

Division of Environmental Health


Date Released: 7/16/2009
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 areas to take precautions to avoid contact with blue-green algae.

We are aware of nine dog deaths that occurred shortly after contact with fresh water bodies in Humboldt and Mendocino Counties which may have been caused by blue-green algae poisoning from 2001-2004. Five dogs died after swimming in Big Lagoon in 2001, while four dogs died after swimming in the South Fork Eel River in 2002 and 2004. A toxin associated with a type of blue-green algae was found in the stomachs of two of the dogs who swam in the South Fork Eel River.

On Copco and Irongate Reservoirs on the Klamath River in Siskiyou County, very large blooms of another type of blue-green algae, Microcystis, and its toxin have been documented over the past few years. This algae also has been found in smaller but still significant amounts below the reservoirs all the way to the Klamath River mouth.

Blue-green algae can look like green, blue-green, white or brown scum, foam or mats floating on the water. Usually it does not pose a hazard to animals or people. However, under certain conditions (such as when the water is warm with abundant nutrients) blue-green algae can grow more rapidly than usual. This can result in floating algal masses or “blooms” that can produce natural toxins that are very potent.

Exposure to these toxins during water recreation can cause eye irritation, allergic skin rash, vomiting, diarrhea, and cold and flu-like symptoms in humans.

Pets and livestock are most likely to be affected by blue-green algal toxins. Although there have been no medically documented reports of human illnesses caused by the algae in Humboldt County, people could be affected by the toxins. Children are most vulnerable since they tend to ingest more water while swimming or playing, and their smaller body size makes them more subject to the effects of the toxins.

The Humboldt County Department of Health and Human Services recommends these precautions to help prevent illnesses or other adverse reactions:
• Keep pets and livestock from swimming in or drinking water containing algal scums or mats.
• Everyone, but especially children, should avoid wading and swimming in water containing algal scums, mats or blooms. In particular, avoid swallowing or inhaling water spray in an algal bloom area
• If no algal scums or mats are visible, you should still warn young children not to swallow any water.
• Fish should be consumed only after removing the guts and liver and rinsing fillets in tap water.
• Get medical treatment right away if you think that you, your pet, or livestock might have been poisoned by blue-green algae toxins.

Warm, slow-moving waters with lots of nutrients are most likely to experience blue-green algae blooms. Two nutrients required by algae are phosphorous and nitrogen. These are found in fertilizers, animal waste, and human (septic system) waste. Excessive pumping of lakes, streams or rivers can cause the water to stagnate and heat up. People can take the following measures to prevent algal blooms in our waterways:

• Minimize the use of water, fertilizers and pesticides on your property. Don’t apply more than the recommended amounts of fertilizers or pesticides, and conserve water with drip irrigation, etc.
• Recycle or dispose of any “spent” pre-fertilized soil that has been used for intensive growing. Runoff from this soil can still contain a lot of nutrients that may stimulate algal blooms.
• Operate and maintain your septic system properly. Overloaded or damaged septic systems can increase nutrients in nearby waters. Have your system pumped every three-four years.
• Encourage the growth of native plants around banks and shorelines. Wetland and streamside plants help filter water and don’t require fertilizers or pesticides to stay healthy.
• Prevent surface water runoff from agricultural areas and keep livestock out of surface waters.
• Prevent erosion around construction and logging operations.


Contact the Humboldt County Division of Environmental Health at (707) 445-6215 or 1-800-963-9241 for more information.

If you have questions about medical treatment, call your doctor. For further information on animal health, 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 Public Health website:


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