Harmful Algal Bloom Monitoring in the Southern Sacramento-San Joaquin Delta

The Department of Water Resources (DWR) North Central Region Office (NCRO) Water Quality Evaluation Section (WQES) and the Division of Operations and Maintenance (O&M) provide technical expertise and program support for regulatory compliance, water operations, emergency response, and environmental restoration.

Harmful Algal Blooms (HABs) are large overgrowths of algae in eutrophic marine or freshwater ecosystems that degrade beneficial uses of water resources, from aesthetics to habitat quality to human consumption. The Sacramento-San Joaquin Delta has observed an increasing number of HABs, especially in the South Delta. These HABs have been composed primarily of cyanobacteria, or blue-green algae (BGA). The most prevalent HAB producing cyanobacteria in recent years is the freshwater species Microcystis aeruginosa - a known producer of toxins called microcystins. Microcystins negatively affect the health of aquatic and terrestrial organisms alike, including humans and their pets. In late 2017, the Central Valley Water Resources Control Board (CVWRCB) issues a Section 401 Water Quality Certification for the DWR South Delta Temporary Barriers Projects. This certification required DWR to develop a dataset of surface Microcystis Visual Index (MVI) values during standard water quality station visits. In addition to the MVI, requirements for DWR to collect water samples for phytoplankton enumeration and cyanotoxin analysis began in 2019 and 2022, respectively. Together these data help DWR and CVWRCB to understand the distribution and composition of the algal community in the South Delta and to evaluate the species that contribute to HABs. As a separate project, DWR O&M collects cyanotoxin and taste and odor samples at Clifton Court Forebay and the Harvey O. Banks Pumping Plant to ensure that the water exported from the Delta is safe for use. This dataset provides an ongoing collection of taste and odor and cyanotoxin analysis beginning in 2009 and 2012, respectively.