A recent sampling event confirming dangerous levels of harmful algal toxins identified in Big Lagoon has prompted the North Coast Regional Water Quality Control Board (RWQCB) to recommended posting a public advisory.

Big Lagoon is sampled for algal toxins every two weeks through a federal grant awarded to the Big Lagoon Rancheria. The most recent results from sampling performed on July 31, 2025, showed one of four sampling locations to be well above the “Danger” concentration established by the California Office of Environmental Health Hazard Assessment, prompting the RWQCB and State Water Quality Advisory Council to recommend the advisory be posted.

As the local response agency for harmful algal blooms in Humboldt County, the Department of Health & Human Services, Division of Environmental Health (DEH), in accordance with voluntary statewide guidance, is advising the public to avoid water contact activities in Big Lagoon until such time as algal toxin levels are below hazardous thresholds.

Although only one of the four sampling locations exceeded the “Danger” threshold, state guidance recommends posting the entire water body.

Benjamin Dolf, a Supervising Environmental Health Specialist with DEH, said, “It’s important to note that blooms are very dynamic, they form, move and dissipate very rapidly, so sampling only provides a snapshot of waterbody conditions at that time. It’s safer for the public to be aware that blooms could occur anywhere throughout the water body.”

Click on the link for a complete map of locations of harmful algae blooms and advisories: (this link)..

The full text of the advisory from the RWQCB and State Water Quality Advisory Council posted for Big Lagoon can be read below.

“Advisory Recommendations: STAY OUT OF THE WATER. Do not touch scum in the water or shore. Do NOT let pets go in the water, drink the water, or eat scum on the shore. Do not eat shellfish from this waterbody.

Report Details: Advisory applies to the full extent of the lake or reservoir (lake-wide advisory) and is not limited to the location symbolized by this report. Advisory based on presence of harmful algal bloom and water testing that detected cyanotoxins. Alert! High concentration of one or more cyanotoxins measured at this site indicating elevated health risk to humans and animals. Updates to this report are provided by a routine water monitoring program conducting site visits at this waterway, refer to Organization field above for more information.

The exact location, extent and toxicity of the reported bloom may not be accurate and may not be affecting the entire waterbody.”

Big Lagoon is not the only location where harmful algal blooms have been observed. Recent reports have also been received for the south fork of the Eel River near Redway and at Richardson Grove State Park in Garberville.

Typically, harmful algal bloom warnings are issued between late July and early August, coinciding with abundant sunlight and warm water temperatures. Depending on weather conditions, bloom conditions could continue into October.

Harmful algal blooms can occur in any freshwater body. Caused by multiple species of what are called cyanobacteria, they can look like dark green, blue-green, black, orange or brown scum, foam or mats on the riverbed or floating on the water. Warm water and abundant nutrients can cause cyanobacteria to grow more rapidly than usual causing “blooms.” These blooms are termed “harmful algal blooms.” Most cyanobacteria do not affect animals or people, however, a small number of cyanobacteria species are capable of producing toxins that can be harmful to animals and humans. 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.

During this time of year, officials recommend the following guidelines for recreational users of freshwater areas:

• Keep children, pets and

• Adults should also avoid

• If no algal scums or mats are

• Fish should be consumed only

• Never drink, cook with or

• Get medical attention immediately if you think that you, your pet or livestock might have been

• Join or support one of the many watershed and river organizations.

To learn more about cyanobacteria and other algal blooms , visit the state of California’s website at mywaterquality.ca.gov/habs/index.html.

To learn more about cyanobacteria and algae on the South Fork Eel River, visit this link..

To report a bloom, e-mail CyanoHAB.Reports@waterboards.ca.gov or call 844-729-6466 (toll free). Blooms can also be reported via the “bloomWatch” app which is available for free download on iTunes or Google play.

For information on conditions occurring within Humboldt County, contact the Division of Environmental Health at 707-445-6215 or 800-963-9241 (toll free). Photos of suspected blooms can also be emailed to envhealth@co.humboldt.ca.us.