Warning Issued About Blue-green Algae in Humboldt and Mendocino


Blue-green algae from stock photo. [Photo by Pseudopanax at English Wikipedia via Wikimedia Commons]

Press release from Humboldt County Department of Health & Human Services:

Typically, algae warnings come out between late July and early August, coinciding with low flows and sustained high temperatures in the inland areas. These factors, coupled with drought conditions, may cause blue-green algae to grow earlier than usual.

Human activities can have a big effect on nutrient and water flows in rivers, streams and lakes. Nutrients found in fertilizers, animal waste and human waste can stimulate blooms. Excessive water diversions can also increase water temperatures and reduce flows. People can take the following measures to prevent algal blooms in our waters:

  • Be conservative with the use of water, fertilizers and pesticides on your lawn, garden or agricultural operation.
  • Avoid nutrient runoff by recycling any “spent” soil that has been used for intensive growing by tilling it back into gardens, or protect it from rainfall.
  • Create shade and filter out nutrients by planting or maintaining native plants around river banks.
  • Inspect and pump out septic systems every three to four years.
  • Prevent surface water runoff from agricultural and livestock areas.
  • Prevent erosion around construction and logging operations.

Blue-green algae can be present in any fresh water body. It looks like dark green, blue-green, orange or brown scum, foam or mats floating on the water. Most blue-green algae does not affect animals or people, however, warm water and abundant nutrients can cause blue-green algae to grow more rapidly than usual. These floating algal masses or “blooms” can produce natural toxins that are very potent. Dogs and children are most likely to be affected because of their smaller body size and tendency to stay in the water for longer periods of time.

While the presence of blue-green algae toxins has been previously confirmed in some water bodies within Humboldt and Mendocino counties including the South Fork Eel, Van Duzen and Trinity rivers, it is difficult to test and monitor the many miles of our local rivers with conditions that may vary. Most algal blooms in California contain harmless green algae, but it is important to stay safe and avoid contact.

To learn more about the occurrence and appearance of blue-green algae on the South Fork Eel River, see the Eel River Recovery Project Toxic Algae Factsheet http://eelriverrecovery.org/documents/cyanobacteria%20factsheet_Mar26_FINAL.pdf.

DHHS, Mendocino EH, and NCRWQCB officials recommend the following guidelines for recreational users of freshwater areas:

Keep children, pets and livestock from swimming in or drinking water containing algal scums or mats.
Adults should also avoid wading and swimming in water containing algal blooms. Try not to swallow or inhale water spray in an algal bloom area.
If no algal scums or mats are visible, you should still carefully watch young children and warn them not to swallow any water.
Fish should be consumed only after removing the guts and liver and rinsing fillets in tap water.
Never drink, cook with or wash dishes with water from rivers, streams or lakes.
Get medical attention immediately if you think that you, your pet, or livestock might have been poisoned by blue-green algae toxins. Be sure to tell the doctor about possible contact with blue-green algae.
Join or support one of the many watershed and river organizations.
For more information or to report unusual blooms or conditions occurring within Humboldt County, contact Humboldt County Environmental Health at 707-445-6215 or 1-800-963-9241. Photos of suspected blooms can be emailed to envhealth@co.humboldt.ca.us.

To report unusual blooms or conditions occurring within Mendocino County contact 707-234-6625.

More details about blue-green algae are available at the California Department of Public Health’s website at http://www.cdph.ca.gov/healthinfo/environhealth/water/Pages/bluegreenalgae.aspx.


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  • I found the cure for toxic blue-green algae on google…

    “Excessive phosphorus in the water from fertilisers, stormwater and other contaminants causes the algae to flourish, while global warming encourages even more rapid growth.

    A number of chemical treatments and mechanical solutions such as dredging or filtration can be used, but their shortcomings include environmental damage, difficulty of use, destabilisation of the pH level of water, short-term results, high cost and the lack of approval for some in many countries.

    A breakthrough has come with a natural product, Phoslock, which was developed by Australia’s CSIRO (Commonwealth Scientific and Industrial Research Organisation) and commercialised by Phoslock Water Solutions Limited (PWS). Phoslock is now cleaning up rivers and lakes in many countries quickly, effectively and at reasonable cost.”

    link= https://en.wikipedia.org/wiki/Phoslock

    Phoslock appears to be modified bentonite clay. Might not be good for spawning fish. Maybe there is some scientific genius out there that can tell us if this is a good idea.

    • Hey Ernie. I’ve also been doing a little research about agricultural applications of certain strains of cyanobacteria. There are places where it is actually being grown in tanks to be used as fertilizer to very positive effect. I have this crazy idea that local gardeners could harvest all that free plant food, improving water quality along the way. More research is required.

      Regarding bentonite, I think you’re probably right about danger to spawning fish. I’d be hesitant to add anything to waterways that might contribute to siltation, but maybe it’s ok for lakes and ponds. Actually, I believe bentonite is used to stop ponds from leaking as well.

      • fortunatoarriza

        Algae is what it eats.our runoff is not good for that.sewage either.the people up river must be removed,or trained (forced)to cultivate algaes on inland sea plankton ( elementcomplete).the algae and bacterium (likespirulina)grown on co2,sunlite,inland sea phytoplankton , exausts a waste of pure oxygen.and stop putting sewage on land.for organic.it,though sterilized is correct growth medium and PH for a massive bad bacterium bloom. Ecoli type.if fed good fertilizer.special pot fertilizers are like batguano,from organic orange sewage fertilized nectar fed bat guano.or guano from starving cattle blood.no chemical analysis.cash.tango.fentanyl.

  • I used 2 bales of Barley Straw which I dumped in my pond wired together. They soaked and sank within a week. And it worked, and 3 years later, it’s still working. There is an enzyme in Barley [straw] which eats the algae, and as it disintegrates, provides food for my stocked catfish. Win-win.
    BUT Barley Straw is very hard to find; had to go to the Sacramento Valley…but worth the time, gas, and effort. This tip came from the UC Extension agent. (Phone book.) af

  • It’s official no more going in the river for me. Looks like the northern nights festival needs to be warned.

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