Harmful algal bloom (HAB)

At the end of July 2022, the District received reports of murky water in the Oakland Estuary. The District, in coordination with other regulatory agencies and scientific organizations, collected water samples to determine if the cause was related to a sewage overflow. On August 4, 2022, the District collected samples from three locations in the estuary. The results indicated typical levels of bacterial indicator organisms which confirmed that the discoloration was not due to the introduction of sewage. Microscopic analyses performed by the California Department of Public Health revealed a proliferation of Heterosigma akashiwo, a marine algae species that can cause a harmful algal bloom (HAB) or “red tide.”

At this time, more research is needed to explain why the current HAB occurred and to prevent future algal blooms.

Impact of Nutrients and Ongoing Research in Bay Area
HABs are not common in the Bay and there have not been any blooms of this magnitude in at least the last 40 years. While nutrients contribute to algal blooms, the specific conditions or triggers that caused this event are not known. Nutrient discharge loading from wastewater treatment plants is slightly lower today than the past nine-year average. Ongoing studies conducted by USGS, SFEI, and others will help to better understand the cause and prevent these occurrences in the future.

Since 2014, the District, along with the 37 Bay Area wastewater treatment agencies that comprise the Bay Area Clean Water Agencies (BACWA), has been under a regional watershed permit to address nutrient discharges from wastewater treatment plants. 

The SFEI has made the following observations and potential outcomes on the current HAB:

  • There has been a sharp drop in Chlorophyll-A (measurement quantifying algal quantities), suggesting the bloom is ending or slowing down.
  • Dissolved oxygen (DO) levels have decreased with the lowest levels measured on August 31. If DO levels start to increase, this may also signal the bloom is slowing. Alternatively, if DO levels continue to drop more fish kills will result.
  • The high heat expected during the next few days (September 2-6) may also stimulate more blooms.

EBMUD staff will continue to monitor the situation and support the regulatory, scientific, and nongovernmental organizations working to investigate the causes of this algal bloom. The District will also continue to contribute to the ongoing scientific studies and collaborate with the regulatory agencies to ensure that ratepayer dollars invested in any future nutrient removal infrastructure achieve the desired benefits for the Bay ecosystem.

Exerpt of memo published September 1,  2022, see link to full memo below.

Document Type Size
Harmful Algal Bloom In The San Francisco Bay PDF <1 MB