In 2022, 60 incidences of harmful algal blooms were voluntarily reported in the Sacramento-San Joaquin Delta.

The Measure

Spatial coverage of freshwater harmful algal blooms (HABs) in select waterbodies in the Delta is reduced.

  • Expectations

    Spatial coverage of freshwater harmful algal blooms (HABs) in select waterbodies in the Delta is reduced.

  • Performance Metrics

    • Spatial coverage (acres) of Microcystis sp. cell concentration equivalents (cells/ml), in Delta waterbodies large enough to use the State Water Resources Control Board mapping tool

Harmful Algal Blooms in the Delta

The map and table below show data from the HABs Incident Reports Map that tracks locations where HABs sightings have been voluntarily reported. A waterbody with no HABs sighting does not mean that a bloom was not present. 

The map below displays the HABs incidences during the 2022 season. Clicking on the points will show the waterbody name. Additional information such as the advisory levels and the date of the reported HABs incident will be displayed at a later date. Data retrieved were as of December 2022. For more recent updates, visit the link labelled "HABs Incident Reports Map" above.

Trigger levels for posting planktonic advisory signs and description of advisory levels:

Advisory Level Description
Caution Harmful algae may be present  in this water.
Warning Toxins from algae in this water can harm people and kill animals
Danger Toxins from algae in this water can harm people and kill animals.

Additional information on advisory and trigger levels can be found on the California Cyanobacteria and Harmful Algal Bloom Network’s (CCHAB) website.

Harmful Algal Blooms Sightings

The table shows voluntary reported incidences of harmful algal blooms since the summer of 2016.

Next Data Update: This visualization will be updated at the end of the year in December 2022.

Algae are natural components of marine and freshwater ecosystems and form the foundation of most aquatic food chains. However, when blue-green algae, also known as Cyanobacteria, is present during an algae bloom event, it has the potential to be harmful to humans and wildlife (hence Harmful Algal bloom, HABs). Blue-green algae is often confused with green algae because both may produce dense mats, reduce oxygen levels, affect odor, and/or impede recreation; however green algae generally do not produce toxins. Blue green algae or cyanobacteria on the other hand, has the potential to produce harmful toxins (cyanotoxins). An overview of cyanotoxins and it's different species can be found on the Environmental Protection Agency's website.

HAB events occur naturally due to environmental factors such as nutrient levels, water flow and chemistry, algal species composition, temperature, and sunlight but may be exacerbated due to human activities such as increased nutrient pollution, invasive species, and reduced water flows. Climate change may also be contributing to the increase in HAB events. This is especially important in California and the Delta due to the effects of climate change which includes prolonged droughts and warmer average temperatures.

Monitoring harmful algal blooms in the Delta will assist in the evaluation of risk to human and aquatic health, as well as provide better understanding of connections and factors promoting or maintaining harmful algal blooms.

On September 2019, AB834 -- Freshwater and Estuarine Harmful Algal Bloom Program was passed.

In summary, the bill requires the State Water Resources Control Board (state board) to:

  1. Establish a Freshwater and Estuarine Harmful Algal Bloom Program to protect water quality and public health from harmful algal blooms.
  2. Coordinate immediate and long-term algal bloom event incident response,
  3. Conduct and support algal bloom field assessment and ambient monitoring at State, watershed, and site specific waterbody scales,
  4. Post information on or before July 1, 2021 on their website regarding algal bloom incidents and responses, among other things, in the state during the previous 3 years.
  5. Authorize the state board, if it determines an algal bloom event is an emergency, as defined, to enter into contracts to aid in incident response without meeting the conditions prescribed for personal services contracts under the State Civil Service Act, including the requirement for a competitive bidding process, or any other competitive bidding requirements under existing law.

Full text of AB834 can be found at

In 2019, State Water Resources Control Board and the San Francisco Estuary Institute released a satellite imagery tool which estimates the amount of cyanobacteria in large water bodies calculated in satellite imagery. It includes approximately 250 water bodies in California. It is designed as a screening level analysis tool, which can prompt field verification and sampling for local and state agencies to confirm if cyanotoxins are present. Additional important information about the satellite tool from the CCHAB portal:

  • The map shows estimates of cyanobacterial abundance near the surface of a water body.
  • The map does not show any information about toxin concentrations and public health advisories.
  • The map shows data collected over a 10-day window and does not display real-time conditions at a water body.
  • All data on the map are currently considered provisional.

As satellite imagery improves, the quality of data will also likely increase overtime. In the future, this tool will be used in assessing this performance measure.

Each chapter of the Delta plan includes strategies to achieve the goals of the plan. These strategies are general guidance on achieving the objective laid out in the plan and in the Delta Reform Act of 2009. Associated with these strategies are recommendations. The recommendations describe more specific and implementable actions to support the achievement of Delta Plan strategies. Strategies and recommendations may also have associated performance measures. Delta Plan performance measures track progress in achieving desired outcomes for the Delta Plan. Below are the strategies and recommendations associated with this performance measure.

Delta Plan Strategy

  • Improve environmental water quality
  • Require Delta-Specific water quality protection

Delta Plan Recommendations

  • Protect beneficial uses
  • Identify Covered Action impact
  • Special water quality protections for the Delta
  • Completion of regulatory processes, research, and monitoring for water quality improvements
  • Implement Delta Regional Monitoring Program
  • Evaluate wastewater recycling, reuse, or treatment
  • Manage dissolved oxygen in Stockton Deep Water Ship Channel
  • Manage dissolved oxygen in Suisun Marsh

Spatial coverage (acres) of Microcystis sp. cell concentration equivalents (cells/ml), in Delta waterbodies large enough to use the State Water Resources Control Board mapping tool (e.g., Discovery Bay; South Delta along Grantline Canal and Old River surrounding Fabian Tract; Big Break Regional Shoreline; and San Joaquin River between Antioch and Stockton) with densities of 100,000 cell/ml or greater, evaluated annually.


Spatial coverage (acres) based on satellite images during the period of 2016–2017


Target to be achieved by 2034:

  • Zero acres of waterbodies with densities of 100,000 cells/ml

Data is retrieved from the HAB Incident Reports Map website where HAB sightings are voluntary reported. Data is then filtered to only include water bodies within the legal Delta area.

Data Source:

HABs incident reports map

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