Harmful Algal Blooms in California Waters – Seminar Examines Impact on Tribes, Communities, and the Environment

For Immediate Release 9/13/23

For more information, contact: 
Brian Smith, (415) 320-9384, brian@bpspr.com

MacKenzie Owens, (925) 282-5459, mackenzie@restorethedelta.org

Stockton, CA – On September 13, 2023, California tribal governments and environmental advocacy organizations held an online seminar to explore how Harmful Algal Blooms (HABs) impact communities, tribes, and fish species that depend on clean, flowing rivers and healthy estuaries. Participants in the seminar included: Shingle Springs Band of Miwok Indians, Restore the Delta, San Francisco Baykeeper, and the University of North Carolina at Chapel Hill.

The seminar focused on harmful algal bloom impacts throughout the San Francisco Bay and the Sacramento-San Joaquin Delta Estuary. A recording of the full seminar will soon be available on the Restore the Delta YouTube page

This seminar presented data and findings on HABs outbreaks throughout the San Francisco Bay-Delta Estuary since 2020. Experts highlighted the difference between freshwater HABs and saltwater HABs, and discussed the importance of San Francisco Bay nutrient discharge and Delta freshwater flows via a new data analysis. The seminar speakers also provided documented scientific findings on the link between HABs and air pollution, and covered Tribal water use challenges with HABs-infested and polluted waters along the Feather River.

James Sarmento, Executive Director of Cultural Resources, Shingle Springs Band of Miwok Indians
James described the ongoing effects that Harmful Algal Blooms in waterways create for Tribal water use issues, including impeding ceremonies and activities. Specifically, he discussed how HABs diminish the ability of youth and elders to participate in cultural practices and daily activities with Tribal members.

“We’ve recently had several events canceled from concerns about the water quality due to HABs. Being able to have events and ceremonies out on the water is important for transferring tribal knowledge. For example, HABs negatively impact a tribal member’s ability to obtain basket weaving materials and other regalia materials.”

Spencer Fern, Delta Science Program Manager, Restore the Delta
Spencer discussed freshwater HABs in the Delta with specifics from testing sites in Stockton. This year, his team hasn’t seen any blooms. Fern shared flowcharts from the years 2019-2023 for the summer months to reference high flow in 2023 for the main reason that blooms haven’t formed this year. He compared other factors from each year and compared to other wet years, snowpack compared to rainfall.

“The one thing that’s different from last year to this year is the increased flow down the main stem of the San Joaquin River, which is one of the few factors we can control to mitigate drought years experienced regularly in Stockton.”

Ian Wren, Staff Scientist, San Francisco Baykeeper
Ian presented the differences with Red Tides and how nutrients from wastewater treatment plants are the primary mechanism for HABs formations in the Bay area. San Francisco Baykeeper is also working on a new permit for HABs in the Bay Area.

“Harmful algal blooms in the Delta are distinct from the growing problem in San Francisco Bay. In simple terms, to tackle harmful algae in the Bay, we need to cut back on excess nutrients from wastewater treatment plants. The challenge is many of these plants were originally built without a focus on reducing nutrient levels.”

Zach Gigone, Environmental Scientist, Shingle Springs Band of Miwok Indians
Zack talked about the Harmful Algal Blooms testing program the Tribe has established with Restore the Delta and the State Water Board. He explained what he has seen out in the field and the results of their testing.

“We [Shingle Springs Band of Miwok Indians] conduct regular testing for cyanotoxins resulting from HABs during the summer months. We have concerns about tribal youth and elders, as well as pets, being exposed to affected areas since it can be deadly for them to ingest or inhale these particles. In past summers, HABs have been found in a couple of ancestral sites along the Sacramento River, raising concerns about future events.”

Haley Plaas, Environmental Science & Engineering PhD Student, University of North Carolina, Chapel Hill
Haley highlighted how Harmful Algal Blooms can be connected to air quality and what scientific research and projects she conducted in order to link these two issues together. Recently, her work alongside fellow researchers was published in ACS Earth and Space Chemistry, detailing the aerosolization of cyanobacterial harmful algal blooms. 

“My team and I have been researching how HABs impact air quality. Our findings in the Delta suggest that gasses that sometimes evaporate off toxic blue-green algal blooms can lead to aerosol formation in the atmosphere, forming particulate matter that is unhealthy to inhale.”


The Bay-Delta watershed has experienced numerous encounters with Harmful Algal Blooms (HABs) in recent years. HABs threaten cultural practices, the environment, and general ways of life. Tribes from the Bay-Delta watershed have had to forgo ceremonial and cultural activities as HABs have raised public health concerns with the contamination of water, fish, and plants along embankments. Environmental Justice communities are suffering from the proliferation of HABs, excluding them from safely recreating on or near waterways due to resulting air and water pollution. Fish and wildlife are in distress from the depletion of oxygen resulting from HABs dissipation. Essentially, HABs are an environmental justice and public health issue. To ensure the safety of tribes, communities, and wildlife, the State Water Board must implement an updated and proper Bay-Delta plan, with more flows essential to the mitigation of HABs.


Fish-killing toxic algae bloom has left San Francisco Bay for now – San Francisco Chronicle 8/17/23

California water agency under investigation for discriminating against tribes, people of color – Cal Matters 8/9/23

Environmental groups push for increased river flow in wake of toxic algal bloom in Delta waterways – ABC 7 News 10/26/22


HABs Report Map – The State Map for HABs reporting and logging

Archived Data from HABs Report Map – Pre-Labor Day Report of a HAB outbreak in Stockton 2019

Flowcharts for HABs in Stockton – Compiled by Spencer Fern, Restore the Delta’s Delta Science Program Manager

HABs Seminar Slides – Slides presented by Spencer Fern and Haley Plaas

Research Paper: Temperature-Dependent Growth Characteristics and Competition of Pseudanabaena and Microcystis – “The optimal temperature range of Microcystis is 25 to 35 °C” (77 to 95 °F)

Research Paper: Managing a Cyanobacteria Harmful Algae Bloom “Hotspot” in the Sacramento – San Joaquin Delta, California – “The entire study area showed signs of classical hypereutrophication, with nitrogen and phosphorus available in non-limiting amounts.”

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