Policies and Guidelines

Currently there are no U.S. federal guidelines, water quality criteria and standards, or regulations concerning the management of harmful algal blooms in drinking water under the Safe Drinking Water Act (SDWA) or in ambient waters under the Clean Water Act (CWA). However, several countries outside the U.S. do have various values that serve as guidelines or thresholds for certain management actions.

What is the regulatory status of HABs in the U.S.?

The SDWA requires the EPA to 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 three drinking water CCLs (CCL 1 of 1998, CCL 2 of 2005 and CCL 3 of 2009). Based on toxicological, epidemiology and occurrence studies, the EPA Office of Ground Water and Drinking Water has focused on 3 of the over 80 variants of cyanotoxins reported, recommending Microcystin congeners LR, YR, RR and LA, Anatoxin–a and Cylindrospermopsin for further research activities. The EPA uses the Unregulated Contaminant Monitoring Rule (UCMR) program to collect data for contaminants suspected to be present in drinking water that do not have health–based standards.

The absence of standardized analytical methods for individual toxins has prevented the EPA from including cyanobacterial toxins in the UCMR. Due to this factor and to the absence of certified toxin standards to support analyses and the lack of capacity to deal with multiple toxin congeners, EPA has not made regulatory determinations or established any guidelines for cyanobacteria and their toxins in drinking water.

The Harmful Algal Bloom and Hypoxia Amendments Act (HABHRCA) of 2013 requires the National Oceanic and Atmospheric Administration (NOAA) to have primary responsibility in advancing the scientific understanding and ability to detect, monitor, assess, and predict HAB and hypoxia events in marine and freshwater. The bill further delineates the role of various members of the Interagency Task Force on Harmful Algal Blooms and Hypoxia. Furthermore, the 2013 bill expands the Task Force's functions, emphasizing increased forecasting, monitoring and observation efforts; further research on the health and ecological effects of HABs; and greater transparency and communication regarding the specific findings of the Task Force.

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

In 1998, The World Health Organization (WHO) released a provisional drinking water guideline for microcystin-LR, excluding other known cyanotoxins since there was insufficient data to derive guideline values for these toxins. The WHO guidance value for drinking water is:

Cyanotoxin Drinking  Water Provisional Guideline
Microcystin-LR 1 µg/L

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 microcystins are:

Relative Probability of Acute Health Effects Cyanobacteria (cells/mL) Microcystin-LR (µg/L) Chlorophyll-a (µg/L)
Low < 20,000 <10 <10
Moderate 20,000-100,000 10-20 10-50
High 100,000-10,000,000 20-2,000 50-5,000
Very High > 10,000,000 >2,000 >5,000

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 three states in the U. S.:

State Drinking Water Guidance/Action Level
Minnesota Microcystin-LR: 0.04 µg/L
Ohio Microcystin: 1 µg/L
Anatoxin-a: 20 µg/L
Cylindrospermopsin: 1 µg/L

Saxitoxin: 0.2 µg/L
Oregon Microcystin-LR: 1 µg/L
Anatoxin-a: 3 µg/L
Cylindrospermopsin: 1 µg/L

Saxitoxin: 3 µg/L

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

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 or the Monitoring Recreational Freshwaters paper by Jennifer L. Graham, Keith A. Loftin, and Neil Kamman (2009). Guidance values for recreational waterways have been adopted by twenty states in the U.S.:

State Recreational Water Guidance/Action Level Recommended Action
California Microcystin: 0.8 µg/L
Anatoxin-a: 90 µg/L
Cylindrospermopsin: 4 µg/L
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)
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: 8µg/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 Microcystin provisional action level: 6µg/L Advisory/Closure
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

Interagency, International Symposium on Cyanobacterial Harmful Algal Blooms
US EPA Contaminant Candidate List (CCL) and Regulatory Determinations
US EPA Creating a Cyanotoxin Target List for the UCMR (PDF) (17 pp, 110K; About PDF) 
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
Health Canada Guidance for cyanobacterial Toxins – Microcystin-LR in Drinking Water
Health Canada Guidelines for Canadian Recreational Water Quality

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

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