Guidelines and Recommendations

On this page:

What is the regulatory status of HABs, cyanobacteria and cyanotoxins in the U.S.?

Harmful Algal Bloom and Hypoxia Research and Control Amendments Act (HABHRCA)

You will need Adobe Reader to view some of the files on this page. See EPA’s About PDF page to learn more.

The Harmful Algal Bloom and Hypoxia Research and Control Amendments Act of 2014 (also known as HABHRCA) (PDF) (9 pp, 210 K) requires the National Oceanic and Atmospheric Administration (NOAA) and USEPA to advance the scientific understanding and ability to detect, monitor, assess, and predict HAB and hypoxia events in marine and freshwater in the U.S. These act also requires to maintain and enhance a national program to control and mitigate harmful algal bloom and hypoxia events, delineates the role of the Task Force (Interagency Working Group or IWG), and to develop reports and plans to reduce the likelihood of HABs formation and to mitigate their damage. For more information and to see the published reports by the IWG please refer to:

Safe Drinking Water Act: CCL and Drinking Water Protection Act

Candidate Contaminant List (CCL)

The SDWA requires that once every five years EPA publish a list of unregulated contaminants that are known or expected to occur in public water systems in the U.S. that occur at a frequency and at levels of public health concern and where there is a meaningful opportunity for health risk reduction. This list is known as the Contaminant Candidate List (CCL). The EPA’s Office of Water has listed cyanobacteria and cyanotoxins on the CCL 1 (1998), CCL 2 (2005) and based on toxicological, epidemiology and occurrence studies, included specifically anatoxin-a, cylindrospermopsin, and microcystin-LR, on CCL 3 (2009) and the CCL 4 (2016).

Unregulated Contaminant Monitoring Rule

The SDWA requires that once every five years EPA issue a new list of no more than 30 unregulated contaminants to be monitored by public water systems (PWSs). Ten (10) cyanotoxins were included in the fourth Unregulated Contaminant Monitoring Rule (UCMR 4), proposed on December 11, 2015 to be monitored between 2018 and 2020 using analytical methods developed by EPA and consensus organizations. This monitoring provides a basis for future regulatory determinations and, as warranted, actions to protect public health.

Drinking Water Protection Act

The Drinking Water Protection Act, also known as H.R. 212 (PDF) (3 pp, 202 K), requires EPA to develop and report to Congress a strategic plan outlining the risks to human health from drinking water provided by public water systems contaminated with algal toxins and to recommend feasible treatment options, including procedures and source water protection practices, to mitigate any adverse public health effects of algal toxins. EPA developed, and submitted to Congress, the Algal Toxin Risk Assessment and Management Strategic Plan outlining how the Agency will continue to assess and manage algal toxins in drinking water.

What are the health-based standards or guidelines for cyanobacteria/cyanotoxins in drinking water?

Health Advisories and Health Effect Support Documents for Cyanotoxins

Under the SDWA, EPA may publish Health Advisories (HAs) for contaminants that are not subject to any national primary drinking water regulation 42 § 300g-1(b)(1)(F)Exit. EPA develops HAs to provide information on the chemical and physical properties, occurrence and exposure, health effects, quantification of toxicological effects, other regulatory standards, analytical methods, and treatment technology for drinking water contaminants. HAs describe concentrations of drinking water contaminants at which adverse health effects are not anticipated to occur over specific exposure durations (e.g., one-day, ten-days, several years, and a lifetime). HAs also contain a margin of safety to address database uncertainties. HAs serve as informal technical guidance to assist federal, state and local officials, as well as managers of public or community water systems in protecting public health when emergency spills or contamination situations occur.

In 2015, EPA developed Health Advisories (HA) for the following cyanobacterial toxins:

These HAs are not regulations and should not be construed as legally enforceable federal standards. HAs may change as new information becomes available.

Cyanotoxin Drinking  Water Health Advisory (10-day)
Bottle-fed infants and pre-school children School-age children and adults
Microcystins 0.3 µg/L 1.6 µg/L
Cylindrospermopsin 0.7 µg/L 3 µg/L

EPA also developed Health Effect Support Documents (HESD) for microcystins and cylindrospermopsin, and also for anatoxin-a. The HESDs constitute a comprehensive review of the published literature on the chemical and physical properties of these toxins, the toxin synthesis and environmental fate, occurrence and exposure information, and health effects.

As a companions to the HAs, EPA also developed a support document entitled Recommendations for Public Water Systems to Manage Cyanotoxins in Drinking Water for states and utilities to assist them as they consider whether and how to manage cyanobacterial toxins in drinking water. The recommendations in this document are intended to assist public drinking water systems (PWSs) manage the risks from cyanobacterial toxins in drinking water, including information and a framework that PWSs can consider in their cyanotoxin risk management efforts.

In 1998, The World Health Organization (WHO) released a provisional drinking water guideline for microcystin-LR of 1µg/L, excluding other known cyanotoxins since there was insufficient data to derive guideline values for these toxins.

Several U.S. states have implemented standards or guidelines that apply to cyanotoxins and cyanobacteria in drinking water using risk assessment methods and the guidelines provided by the WHO for recreational waters. Guidance values for drinking water have been adopted by four states in the U.S.

 State  Drinking Water Guidance/Action Level
Minnesota Microcystin-LR: 0.1 µg/L; Anatoxin-a: 0.1 µg/L

Do Not Drink – children under 6 and sensitive populations (pregnant women, nursing mothers, those receiving dialysis treatment, the elderly and immune-compromised individuals)
Microcystin: 0.3 µg/L
Anatoxin-a: 20 µg/L
Cylindrospermopsin: 0.7 µg/L
Saxitoxin: 0.2 µg/L

Do Not Drink – children 6 and older and adults
Microcystin: 1.6 µg/L
Anatoxin-a: 20 µg/L
Cylindrospermopsin: 3.0 µg/L
Saxitoxin: 0.2 µg/L

Do Not Use (based on the Recreational No Contact Advisory thresholds)
Microcystin: 20 µg/L
Anatoxin-a: 300 µg/L
Cylindrospermopsin: 20 µg/L
Saxitoxin: 3 µg/L

Oregon Ages 5 years and younger:
Microcystin: 0.3 µg/L
Anatoxin-a: 0.7 µg/L
Cylindrospermopsin: 0.7 µg/L
Saxitoxin: 0.3 µg/L

Microcystin: 1.6 µg/L
Anatoxin-a: 3 µg/L
Cylindrospermopsin: 3 µg/L
Saxitoxin: 1.6 µg/L
Vermont Microcystin-LR: equal to or greater than 0.16 µg/L
Anatoxin-a: equal to or greater than 0.5 µg/L
Cylindrospermopsin: equal to or greater than 0.5 µg/L

What are the standards or guidelines for cyanobacteria/cyanotoxin in recreational water?

EPA is developing a Draft Human Health Recreational Ambient Water Quality Criteria and/or Swimming Advisories for Microcystins and Cylindrospermopsin to protect the public from incidental ingestion of these two cyanotoxins during primary contact recreation. For an overview of the draf criteria and other materials please see the Microbial (Pathogen)/Recreational Water Quality Criteria page..

For recreational waters, the WHO concludes that a single guideline value for cyanobacteria or cyanotoxins is not appropriate. Due to the variety of possible exposures through recreational activities (contact, ingestion and inhalation) it is necessary to differentiate between the chiefly irritative symptoms caused by unknown cyanobacterial substances and the more severe health effects due to exposure to high concentrations of known cyanotoxins, particularly microcystins. The WHO guidance values for the relative probability of acute health effects during recreational exposure to cyanobacteria and the probability of microcystins concentrations are:

Relative Probability of Acute Health Effects

Cyanobacteria (cells/mL)

Microcystin-LR (µg/L)

Chlorophyll-a (µg/L)


< 20,000











Very High

> 10,000,000



Many U.S. states have implemented HAB response guidelines in the event of a significant bloom in recreational waterways. These include specific criteria for analyzing the severity of a bloom and the actions—public advisories, posted warnings, waterway or beach closures, among others—that correspond to a bloom that meets a certain threshold. For a summary of the U.S. states with guidance values, see the table below.

 State Recreational Water Guidance/Action Level  Recommended Action
California Caution Trigger Level = MCs: 0.8 μg/L; Anatoxin-a: Detect; Cylindrospermopsin: 1 μg/L
Warning Tier I = MCs: 6 μg/L; Anatoxin-a: 20 μg/L; Cylindrospermopsin: 4 μg/L
Danger Tier II = MCs: 20 μg/L; Anatoxin-a: 90 μg/L; Cylindrospermopsin: 17 μg/L
The trigger level of 0.8 μg/L microcystin prompts increased monitoring and the placement of a caution sign stating that people should stay away from scum and pets and livestock should be kept away from the water and scum.
Microcystins refers to the sum of all measured microcystin variants. Must use an analytical method that detects <1 μg/L anatoxin-a.
Connecticut -Visual Rank Category 1: Visible Material is not likely cyanobacteria or water is generally clear.
-Visual Rank Category 2: Cyanobacteria present in low numbers. There are visible small accumulations but water is generally clear.
-Visual Rank Category 3: Cyanobacteria present in high numbers. Scums may or may not be present. Water is discolored throughout. Large areas affected. Color assists to rule out sediment and other algae.
-Visual Rank Category 3, or blue-green algae cells > 100k/ml: POSTED BEACH CLOSURE (If public has beach access, alert water users that a blue-green algae bloom is present), POSTED ADVISORY (At other impacted access points)
Idaho Surface scum visible and associated with toxigenic taxa*

Sum of all potentially toxigenic taxa ≥100,000 cells/mL

The density of Microcystis or Planktothrix >40,000 cells/mL

*Toxigenic taxa include Anabaena, Microcystis, Planktothrix, Nostoc, Coelosphaerium, Anabaenopsis, Aphanizomenom, Gloeotrichia, Woronichinia, Oscillatoria, and Lyngbya. Additional taxa are known to be potentially toxic and may be added to the list.
Recommend posting by Public Health District (PHD) in conjunction with water body management agency

Recommend posting by PHD in conjunction with water body operator

Recommend posting by PHD in conjunction with water body operator

Illinois Microcystin-LR concentration results approach or exceed 10 µg/L Reporter of HAB event and the local lake management entity will be informed immediately.
Indiana Level 1: very low/no risk < 4 µg/L microcystin-LR
Level 2: low to moderate risk 4 to 20 µg/L microcystin-LR
Level 3: serious risk > 20 µg/L microcystin-LR
Warning Level: Cylindrospermopsin: 5 ppb
Level 1: use common sense practices
Level 2: reduce recreational contact with water
Level 3: consider avoiding contact with water until levels of toxin decrease
Iowa Microcystin ≥ 20 µg/L Caution - bloom present no toxin data available
Warning - when toxin levels exceed 20 µg/L
Kansas PHA: >4 µg/L to <20 µg/L for microcystin or > 20,000 cell/mL to <100,000 cell/mL cyanobacteria cell counts
PHW: > 20 µg/L or > 100,000 cell/mL cyanobacterial cell counts and visible scum present
Public Health Advisory (PHA): avoid contact
Public Health Warning (PHW): all contact with water is restricted

(Louisville District)
Advisory: >20,000 cells/mL of cyanobacteria cell counts

Caution: > 100,000 cells/mL of cyanobacteria cell counts
Advisory: contact discourage, water may be unsafe

Caution: Closure, contact prohibited
Massachusetts 14 µg/L for microcystin-LR and ≥ 70,000 cells/mL for cyanobacteria cell counts Advisory - Avoid contact with water
Nebraska Microcystin ≥ 20 µg/L Health Alert
New Hampshire >50% of cell counts from toxigenic cyanobacteria Public Health Advisory
North Carolina Visible discoloration of the water or a surface scum may be considered for microcystin testing Advisory/Closure
Ohio Microcystin-LR: PHA: 6 µg/L; NCA: 20 µg/L
Anatoxin-a: PHA: 80 µg/L; NCA: 300 µg/L
Saxitoxin: PHA: 0.8 µg/L; NCA: 3 µg/L
Cylindrospermopsin: PHA: 5 µg/L; NCA: 20 µg/L
Public Health Advisory (PHA) - swimming and wading are not recommended, water should not be swallowed and surface scum should be avoided.
No Contact Advisory (NCA) -recommend the public avoid all contact with the water
Oklahoma 100,000 cell/mL of cyanobacteria cell counts and > 20µg/L for microcystin Blue-Green Algae Awareness Level Advisory
Oregon Option 1: Visible scum and cell count or toxicity
Option 2: Toxigenic species >100,000 cells/mL
Option 3: Microcystis or Planktothrix > 40,000 cells/mL
Option 4: Toxin Testing Microcystin: 10µg/L Anatoxin-a: 20 µg/L Cylindrospermopsin: 6µg/L Saxitoxin: 100 µg/L
Public Health Advisory
Rhode Island Visible cyanobacteria scum or mat and/or cyanobacteria cell count > 70,000 cells/mL and/or ≥14 µg/L of microcystin-LR Health Advisories
Texas >100,000 cell/mL of cyanobacteria cell counts and >20µg/L microcystin Blue-Green Algae Awareness Level Advisory
Vermont 4,000 cells/mL cyanobacteria cell counts or ≥ 6µg/L microcystin-LR and the visible presence of cyanobacterial scum
Anatoxin-a ≥ 10 µg/L
Beach Closure
Virginia 5,000 to <20,000 Microcystis cells/mL
20,000 to 100,000 Microcystis cells/mL
> 100,000 Microcystis cells /mL, or > 6 μg/L microcystin concentration, or
Blue-green algal “scum” or “mats” on water surface
Local agency notification; initiate bi-weekly water sampling
Public notification indicating a harmful algal bloom is present in recreational water; initiate weekly sampling
Immediate public notification to avoid all recreational water contact where bloom is present; continue weekly sampling
Washington Microcystin-LR: 6 µg/L
Anatoxin-a: 1 µg/L
Cylindrospermopsin: 4.5 µg/L
Saxitoxin: 75 µg/L
Tier 1. Caution: when a bloom is forming or a bloom scum is visible (toxic algae may be present)
Tier 2. Warning: Toxic algae present
Tier 3. Danger: Lake closed
Wisconsin > 100,000 cells/mL or scum layer Advisory/Closure

More Information

The following links exit the site Exit

Drinking Water Cyanotoxin Risk Communication Toolbox
US EPA Contaminant Candidate List (CCL) and Regulatory Determinations
US EPA Creating a Cyanotoxin Target List for the UCMR
US EPA 2015 Drinking Water Health Advisories for Two Cyanobacterial Toxins Fact Sheet
US EPA Drinking Water Health Advisory for the Cyanobacterial Microcystins Toxins
US EPA Drinking Water Health Advisory for the Cyanobacterial Toxin Cylindrospermopsin
US EPA Health Effects Support Document for the Cyanobacterial Toxin Anatoxin-a
US EPA Health Effects Support Document for the Cyanobacterial Microcystins Toxins
US EPA Health Effects Support Document for the Cyanobacterial Toxin Cylindrospermopsin
US EPA Recommendations for Public Water Systems to Manage Cyanotoxins in Drinking Water
WHO Cyanobacterial toxins: Microcystin-LR in Drinking-water
WHO Toxic cyanobacteria in water: A guide to their public health consequences, monitoring and management
WHO Guidelines for Safe Recreational Waters Volume 1 - Coastal and Fresh Waters

For comments, feedback or additional information, please contact Lesley D'Anglada (, Project Manager, at 202-566-1125.

Top of Page