2021 Recreational Health Advisory Guidance for Harmful Algal Blooms

In 2017, the Environmental Protection Agency (EPA) prepared draft human health guidance on the potential health effects of recreational exposure to microcystin and cylindrospermopsin, two cyanotoxins found in harmful algal blooms. The new guidance uses the latest scientific information on adverse human health effects from exposure to cyanotoxins and cyanobacteria and includes guidance on the health impacts of toxigenic cyanobacteria cell count densities. EPA finalized its guidance in 2019 in the Clean Water Act (CWA) section 304(a) Recommended Human Health Criteria, and Utah incorporated these new thresholds into its 2020 guidance documents.

Local health departments (LHDs) in Utah have the authority to post health advisories and close waterbodies. LHDs use these recreational health thresholds to determine if and when a bloom presents a human health risk. The Division of Water Quality (DWQ) supports LHDs through a monitoring and sampling program that prioritizes waters that are at risk for cyanobacteria blooms, experience high recreational use, or serve as drinking water sources. DWQ interprets and reports sampling results, and along with the Utah Department of Health (DOH), makes recommendations to LHDs on the issuance of recreational health advisories based on sampling data and the best available science.

2021 Guidance Documents

The 2021 Guidance Summary identifies four independent indicators to protect recreational users from adverse health effects from HABs:

  • Toxigenic cyanobacteria cell density
  • Microcystins
  • Cylindrospermopsin
  • Anatoxin-a

If any of these indicators is exceeded, a recreational health advisory is recommended. The Summary also provides a multi-tiered approach to public health advisories.

Health Watch

This is not a formal advisory level but rather an indication that a bloom may exist or become more severe. Increased monitoring is strongly recommended. Indicators may include:

  • Visual observations/reports of a possible bloom
  • Reports of animal or human illness
  • Detection of cyanotoxins or toxigenic cyanobacteria cell density below thresholds

LHDs may wish to caution users about the possibility of bloom and provide specific information about the bloom event.


A Warning Health Advisory is recommended if sampling data confirm exceedance of one or more of the four thresholds.

  • Toxigenic cyanobacteria cell densities above 100,000 cells per milliliter (cells/mL). Note: Human symptoms have been reported between 5,000 and 100,000 cells/mL. LHDs should take into account other contextual information and consider issuing an advisory when cell densities fall between 5,000 and 100,000 cells/mL.
  • Microcystins levels between 8 and 2,000 micrograms per liter (µg/L)
  • Cylindrospermopsin levels greater than 15µg/L. Note: Data are sparse on breakpoints between Warning and Danger thresholds for cylindrospermopsin. LHDs may wish to consult with DWQ and DOH as needed for further information.
  • Anatoxin-a levels from 15 µg/L to 90 µg/L


A Danger Health Advisory is recommended if sampling data confirm exceedance of one or more threshold. Consider closure of the affected waterbody.

  • Microcystins levels greater than 2,000 µg/L
  • Anatoxin-a levels greater than 90 µg/L
  • Depending on contextual information, toxigenic cyanobacteria cell density and/or cylindrospermopsin levels may also warrant a danger advisory. Consult with UDQ and UDOH as needed.
Public Health Advisory Tiers. Click for larger view.

Health Advisories and/or Beach Closures

DOH and DEQ recommend that local health departments (LHDs) use the table and accompanying decision algorithm when determining the appropriate level of health risk and public health action for a given waterbody. If an LHD receives reports of human or animal illness or death that is plausibly linked to cyanobacteria, an immediate public health advisory is recommended.

Once an advisory is issued, the Guidance recommends at least two weeks of measurements indicating the hazard has passed before removing the advisory. See Health Advisory Flowchart for more information.


The HABs Communication Workgroup has developed WARNING and DANGER signs that LHDs may use when issuing a health advisory. A Health Watch sign is available for LHDs that wish to caution users about possible blooms in a waterbody.

Health Advisory Decision Diagram. Click for larger view.
Warning: Blank Logo
Warning: Blank Logo
Warning Sign: Blank Logo
Warning Partial: Blank Logo
Danger: English
Danger: English

Public Comments Received on Updated Guidance

DWQ received four comment letters on the 2020 updates to the HABs guidance thresholds. These comment letters, and DWQ’s response to each, are provided below.

Guidance for Waterbody Sampling

The recommended standard operating procedure (SOP) for collecting samples for HABs and HAB cyanotoxins are described in DWQ’s Standard Operating Procedure for the collection of Phytoplankton Samples during Harmful Algal Blooms. Quick links to relevant portions of the SOP include:

Guidance for Fish and Wildlife Mortality Sampling

The recommended standard operating procedure (SOP) for collecting samples for carcasses of fish and wildlife associated with a HAB event is described in the U.S. Fish and Wildlife Service (FWS) and DWQ Guidance for Fish and Wildlife Mortality Sampling.

Fish Consumption from High Cyanobacteria Count Areas

Cyanotoxins can accumulate in fish in waters with high toxin levels. The highest concentrations are in the organs, particularly the liver, and fat deposits. Muscle tissue typically has lower toxin levels. Fish taken from waters with intermittent blooms are unlikely to have toxin levels in muscle that present a health concern. However, there remains considerable uncertainty about the health effects of fish consumption, particularly from waterbodies that experience frequent HABs.

UDOH and UDEQ recommend carefully cleaning and thoroughly cooking fish harvested from waters where cyanobacteria are present. This includes discarding the guts and skin, eating only the fillets, and rinsing the meat in clean water before cooking.

In 2019, the Division of Wildlife Resources (DWR) added a time-limited emergency amendment to the 2019 Utah Fishing Guidebook that made it illegal for anyone to fish at a Utah reservoir after a Danger Advisory closed the waterbody due to high toxigenic cyanobacteria cell densities. DWR may choose to make it illegal to fish in certain areas in the future if potential health impacts from fishing and consuming fish from the waterbody warrant closure.