California Voluntary Guidance for Response to HABs in Recreational Inland Waters

This voluntary guidance will assist responding organizations, including environmental and public health officials, land and waterbody managers, citizen scientists, and others in responding to inland harmful algal blooms (HABs) in California. Resources specific for PLANKTONIC (water column) HABs and BENTHIC MATS (which typically grow as mats along bottom substrate) are included below. For more information on BENTHIC MATS (also referred to as TOXIC ALGAL MATS for the general public) and how they differ from PLANKTONIC blooms within the water column, check out the FAQs on TOXIC ALGAL MATS page.

This guidance does not address cyanotoxins in drinking water; State Water Board’s Division of Drinking Water provides resources for addressing cyanotoxins in drinking water.

HAB Response Plan Summary and Key Resources

Table 1 below summarizes the current HAB Response Plan, the recommended actions, and key resources available on the California HAB Portal. This response plan can be adapted for a given incident, some steps may occur in a different order or simultaneously.

  Recommended Actions1 and Key Resources

Step 1: Surveillance and General Awareness   

Responding organizations (Water Boards, land/water manager, local health agency and/or collaborator) should visually inspect publicly accessible rivers, lakes, and reservoirs during recreation season for potential HABs, including those in the water column (PLANKTONIC) and mats attached to the bottom, floating, or stranded along the shore (BENTHIC MATS).
Responding organizations can use general awareness signs to inform the public about potential PLANKTONIC HABs or BENTHIC MATS.


Step 2: Initial Discovery and Reporting

Reports of potential HAB occurrences and any potentially related human or animal illnesses should be made to the HAB Hotline (managed by Water Boards) by using any of the following:

Water Board staff will evaluate initial reports and post to the HAB portal incident map as appropriate.


Step 3: Interagency Response Coordination and Communication

As shown in Figure 1 below, Water Boards HAB coordinator coordinate with the reporting party and agency staff in responding to the HAB.
When potential HAB-related human or animal illnesses are reported, staff from an interagency HAB-related illness workgroup follow up to collect additional information and provide assistance. 
If initial results indicate that cyanotoxins are present in a waterbody with a potential drinking water intake, report to the HAB Hotline immediately. Water Boards Div. of Drinking Water will immediately notify the water purveyor.
Downstream users of the impacted waterbody should be informed since cyanobacteria cells and toxins can be transported many miles downstream.


Step 4: Field Screening

Responding organization can use field screening methods for initial determination if cyanobacteria and cyanotoxins are present. As necessary, samples may be collected for lab analysis at this step (refer step 5).
If visual indicators of PLANKTONIC HAB or BENTHIC MATS or a HAB-related illness is suspected, post corresponding advisory sign at the water body to inform recreationalists of potential health risks. Sign posting should be reported to the HAB Hotline.


Step 5: Sampling for Lab Analysis

Responding organization should collect water, scum, or algal mat samples for laboratory analysis consistent with the Field Guide. Contact HAB Hotline to coordinate potential field support and/or laboratory analysis. Refer to Field Guide SOP for sample storage (refrigerated) and short holding time (< 5 days).
Sample submitting party should report lab results to the HAB Hotline. Water Board staff will evaluate and post to the HAB portal map.


Step 6: Posting Advisory Sign

If analyses or observations meet or exceed TRIGGER LEVELS for PLANKTONIC HABs or BENTHIC MATS, the responding organization should initiate coordination regarding sign posting by reporting to the HAB Hotline.
Water Board will recommend that the corresponding ADVISORY sign be posted, and will coordinate posting and notification with the water agency, local health authorities, land and water management agency, and/or local county coordinators. In some circumstances, Regional Water Board staff may post signage.
Public notification by press and social media can be coordinated with the Water Boards, and outreach and communication tools are available.


Step 7: Continue Monitoring During an Advisory

While under an advisory, water should be observed approximately bi-weekly by the responding organization. If observations suggest that the bloom or algal mats are significantly increasing or decreasing, then the responding organization should conduct follow-up monitoring for cyanotoxins and/or cyanobacteria 2.


Step 8: De-posting and Routine Monitoring

Once the visual indicators and/or cyanotoxin concentrations are below the de-posting criteria for PLANKTONIC HAB or BENTHIC MATS for minimum of two consecutive weeks, signage should be removed by the land and water management agency and/or local county coordinators. De-posting actions should be reported to the HAB Hotline. Public notification of de-posting by press and social media can be coordinated with the Water Boards, and outreach and communication tools are available.
Routine monitoring should continue during the recreation season 2.


1Notification and communication is a key component of each step in the process.

2 While this guidance provides a response to current HABs, long-term plans are ultimately necessary to manage, mitigate, and prevent HABs. Contact the SWRCB’s Surface Ambient Monitoring Program (SWAMP), and check out the California Cyanobacterial and Harmful Algal Bloom (CCHAB) Network Mitigation Subcommittee’s Resources for Mitigating HABs page.

Interagency Response Coordination

Reports of HABs or potential HAB-related illnesses are received through the State Water Board’s reporting system. Once received, the report is investigated by the Interagency Task Force in a coordinated response with state and local representatives (see Figure 1 below) and displayed on the HAB incident report map.

Benthic trigger level sign posting process summary
Figure 1. Interagency Response Coordination graphic (see Table 2 below for State agency contacts)

HABs Response Contacts Table

Table 2 below provides contact information for staff at state agencies participating in the interagency task force.

Table 2. State Agency contacts for HAB response and the HAB-related illness workgroup

Organization Contact Information

HAB Hotline, State Water Resources Control Board (State Board)

  • State Board Lead HAB staff;

  • State Board, Interagency Coordination Lead

  • State Board, Division of Drinking Water

View this map to select appropriate district office contact

Regional Water Quality Control Boards (Regional Board) Map

View the map on left to select appropriate region listed below (Regions 1-9)

  • Region 1, North Coast;

  • Region 2, San Francisco Bay

  • Region 3, Central Coast

  • Region 4, Los Angeles

  • Region 5, Central Valley

  • Region 6, Lahontan

  • Region 7, Colorado River

  • Region 8, Riverside

  • Region 9, San Diego

Cal EPA, Office of Environmental Health Hazard and Assessment;

Tracking California / California Department of Public Health

California Department of Fish and Wildlife, Statewide HAB Coordinator (primary contact)
California Department of Fish and Wildlife, Wildlife Health Laboratory (*general info); (bird specialist) (mammal specialist)

* Note that the WIL email will likely change to WHL at some point

Advisory Signs and Posting Guidance for Planktonic HABs

Participating state agencies - State Water Resources Control Board, Office of Environmental Health Hazard and Assessment (OEHHA), and California Department of Public Health (CDPH) - developed these guidelines for PLANKTONIC (water column) blooms. The California Cyanobacteria and Harmful Algal Bloom Network (CCHAB) under the California Water Quality Monitoring Council adopted them as voluntary guidance (not policy or regulation) in 2016, and recommends their use to promote consistency in public notification and risk communication throughout California. A frequently asked questions (FAQs) on HAB signs is available for the general public.

Planktonic HAB Posting Guidance

These trigger levels and decision tree for posting PLANKTONIC advisory signs (Caution, Warning, and Danger) were developed to protect human and animal (dogs and livestock) health from HABs. The trigger levels are based on the following criteria: concentrations of three major cyanotoxins in water, cell count of potential toxin producers, and site specific indicators. For more information on how these levels were derived, refer to Appendix A - Description of cyanotoxin trigger levels in recreational water bodies.

Table 3. CCHAB trigger levels for posting PLANKTONIC advisory signs.

Trigger Levels For Human and Animal Health
Criteria* No Advisory a Caution
(TIER 1)
(TIER 2)
(TIER 3)

Total Microcystins b

< 0.8 µg/L

0.8 µg/L

6 µg/L

20 µg/L


Non-detect c

Detected c

20 µg/L

90 µg/L


< 1 µg/L

1 µg/L

4 µg/L

17 µg/L

Cell Density of potential toxin producers

< 4,000 cells/mL

4,000 cells/mL



Site-specific indicator(s)

No site-specific indicators present

Discoloration, scum, algal mats, soupy or paint-like appearance.

Suspected illness



* Action levels are met when one or more criteria are met.
a For de-posting, all criteria for no advisory must be met for a minimum of 2 weeks. General awareness sign may remain posted and healthy water habits are still recommended.
b Microcystins refers to the sum of all measured Microcystin congeners.
c Must use an analytical method that detects ≤ 1μg/L Anatoxin-a.

Response Decision Tree for Planktonic Blooms
Figure 2. Response Decision Tree for Planktonic Blooms

Planktonic HAB Advisory Signs

The Planktonic HAB advisory signs are available in both English and Spanish, either as an individual signs in a single language or as a combination with both languages on one sign.

Planktonic HAB advisory signs
  • The PDF format provides pre-made planktonic HAB advisory signs and space to insert local agency contact information. The English, Spanish, and English/Spanish combination versions of all three signs (Caution, Warning, Danger) in PDF format are combined into a single file.
  • The PowerPoint format allows customization of signs by deleting individual icon/text message components that are not appropriate for a specific water body, such as messaging specific to an activity that is not otherwise permitted. However, text with each component cannot be changed. Components can be moved to allow more space for local agency contact information (text box at the bottom of each sign). The English and Spanish versions of all three signs (Caution, Warning, Danger) in PowerPoint format are combined into a single file.
  • The individual signs and icons (in PowerPoint format) are also available as supplemental information.

Planktonic General Awareness HAB Signs

The PLANKTONIC general awareness HAB signs below are two templates provided by the US EPA that have been customized for for California.

harmful algal blooms awareness
  • Abbreviated infographic  (PDF)
  • Detailed infographic (PDF) 
  • General awareness signs or infographics can be used to inform the public of the potential for PLANKTONIC HABs, how to identify them, potential symptoms, healthy water habits, and where to find additional resources.
  • These signs can be posted permanently at waterbodies where PLANKTONIC HABs may occur and used in combination with advisory signs triggered by specific visual observations or water column cyanotoxin results as described above.
  • These signs are not intended to replace advisory signs or preclude water testing for cyanotoxins.

Benthic Cyanobacteria (Toxic Algal Mats) Signs and Posting Guidelines

The CCHAB Network Benthic Signage Subcommittee developed signs (general awareness and BENTHIC trigger level) and posting guidelines for BENTHIC MATS, also referred to as TOXIC ALGAL MATS. These resources were reviewed and adopted for use by CCHAB Network in 2020.

posting guidelins

Check for Algae sign
Toxic Algae Alert sign

HAB Outreach and Communication

In addition to signage, other forms of outreach and communication may be appropriate, both during a current incident and to increase awareness of potential HABs and their potential health impacts. Resources available on the CA HABs Portal are summarized below. US EPA also provides general HAB communication tools.

Public notifications and press communications for a current HAB incident

media release

Resources for use with the general public

protect your pets

Resources for use with medical professionals and veterinarians

veterinary resources
  • Doctors and veterinarians may not be familiar with the symptoms of cyanotoxin exposure, potential treatment, and how to report potential HAB-related illnesses in humans, pets, and livestock.  
  • The online pages linked above include resources that can be shared with local medical providers and veterinarians to assist in appropriate diagnosis, treatment, and reporting, and to share with their clients.
  • The HAB-related Illness Tracking webpage summarizes previously reported human and animal illnesses related to HABs in California.