Skip to main content
U.S. flag

An official website of the United States government

Here’s how you know

Dot gov

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

HTTPS

Secure .gov websites use HTTPS
A lock (LockA locked padlock) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

    • Environmental Topics
    • Air
    • Bed Bugs
    • Cancer
    • Chemicals, Toxics, and Pesticide
    • Emergency Response
    • Environmental Information by Location
    • Health
    • Land, Waste, and Cleanup
    • Lead
    • Mold
    • Radon
    • Research
    • Science Topics
    • Water Topics
    • A-Z Topic Index
    • Laws & Regulations
    • By Business Sector
    • By Topic
    • Compliance
    • Enforcement
    • Laws and Executive Orders
    • Regulations
    • Report a Violation
    • Environmental Violations
    • Fraud, Waste or Abuse
    • About EPA
    • Our Mission and What We Do
    • Headquarters Offices
    • Regional Offices
    • Labs and Research Centers
    • Planning, Budget, and Results
    • Organization Chart
    • EPA History

Breadcrumb

  1. Home
  2. Nutrient Pollution

Lakes Presenting Risk for Exposure to Harmful Algal Toxins

(Photo on left) Massive Algal Bloom in the St. Johns River, Florida. Photo by Bill Yates (Photo on right) Sign alerting citizens that an algal bloom in the area has potentially made direct contact with water unsafe. Photo by Mike Tate, Kansas Department of Health and Environment, Bureau of Water, Technical Services Section
Specific Indicators
Documented Nutrient Pollution
  • Nutrient loads and yields
  • Fertilizer
  • Manure
Documented Impacts
  • Hypoxia
  • Harmful algal toxins
  • Groundwater nitrate
  • Assessed and impaired waters
State Actions Underway
  • Limiting loads (Status of Nutrient Requirements for NPDES-Permitted Facilities)
  • Adoption of standards

Nutrient Indicators Dataset Home

About this indicator

One of the potential effects of excess nutrients in lakes is the overgrowth of cyanobacteria, also known as blue-green algae, which produce toxins (cyanotoxins) that are harmful to people’s health and can kill fish, mammals and birds. When the density of such harmful organisms leads to the presence of scum on the lake surface or discoloration of the water, they are known as harmful algal blooms (HABs). The frequency and severity of HABs has been linked to increased nutrient loading from human activities (Lopez et al. 2008), and cyanobacterial HABs are considered one of the clearest indicators of excess nutrient concentrations (Paerl and Fulton, 2006). Cyanobacteria can produce neurotoxins (nervous system), hepatotoxins (liver) and dermatoxins (skin), posing a threat to human health when blooms occur in drinking water supplies. Additionally, cyanotoxins in recreational waters can pose a danger to people, pets, and livestock when they come in contact with the water.

The data presented here pertain to microcystins, and not other algae which may produce toxins. The data for this indicator are the number of lake visits sampled per state for microcystins during EPA’s 2017 National Lakes Assessment, and the number of samples which contained greater than EPA’s national recommended human health recreational criterion of 8 µg/l. When applied as a Clean Water Act section 304(a) water quality criterion, EPA recommends no more than 3 excursions (10-day assessment periods) within a recreational season per year. When used as a swimming advisory, EPA recommends the value not be exceeded on any single day.

Number of state lake visits sampled for microcystins and the number of samples which contained greater than 8 µg/l of microcystins.
State Number of Samples over 8 µg/l Number of Lake Visits
Alabama 0 10
Alaska NA NA
Arizona 0 15
Arkansas 0 10
California 0 26
Colorado 0 25
Connecticut 0 12
Delaware 0 9
Florida 0 18
Georgia 2 13
Hawaii NA NA
Idaho 1 28
Illinois 0 15
Indiana 2 52
Iowa 2 17
Kansas 0 17
Kentucky 0 11
Louisiana 0 16
Maine 0 26
Maryland 0 10
Massachusetts 0 12
Michigan 0 52
Minnesota 2 52
Mississippi 0 16
Missouri 0 19
Montana 0 33
Nebraska 1 30
Nevada 0 17
New Hampshire 0 13
New Jersey 0 13
New Mexico 0 15
New York 0 12
North Carolina 0 15
North Dakota 7 56
Ohio 0 18
Oklahoma 2 32
Oregon 1 51
Pennsylvania 0 18
Rhode Island 0 10
South Carolina 0 11
South Dakota 4 45
Tennessee 0 11
Texas 1 43
Utah 0 24
Vermont 0 12
Virginia 0 23
Washington 0 33
West Virginia 0 10
Wisconsin 1 54
Wyoming 0 21

Note - data should not be used to make statewide estimates of the percent of lakes presenting risk for exposure to microcystins.

Source: EPA's 2017 National Lakes Assessment.

Download the Toxins data table (xlsx) (11.45 KB)

Source of data

  1. U.S. EPA. 2017 National Lakes Assessment: The Third Collaborative Survey of Lakes in the United States. Office of Water and Office of Research and Development. Washington, DC.
  2. U.S. EPA (2022). National Lakes Assessment 2017: Technical Support Document. EA 841-R-22-001. U.S. EPA, Office Water and Office of Research and Development. Washington, DC.

Data source information

Data are from EPA’s 2017 National Lakes Assessment: The Third Collaborative Survey of Lakes in the United States (2022). In this study, EPA conducted a national survey of the condition of lakes, reservoirs and ponds, which included sampling for microcystins. Number of lake visits was obtained from table 2-2 in the 2017 National Lakes Assessment Technical Support Document. At each lake site, a sample was taken at a single station located at the deepest point in the lake, which would be expected to minimize the chance for false positives. Users may download the report and all the raw data directly from EPA’s National Lakes Assessment website Data from the National Aquatic Resource Surveys from the table entitled “National Aquatic Resource Surveys Data.”

What to consider when using these data

The lakes sampled for the 2017 National Lakes Assessment were chosen in a random, probability-based manner. However, while the base funding for the survey provided for the sampling of enough sites to make national and regional scale estimates of lake conditions, most states could not sample enough sites to allow for generation of state-level estimates. Therefore, the data shown here should not be extrapolated to make state-wide estimates of the percent of lakes presenting risk of exposure to microcystins. Users should also consider that the lake samples were collected for the survey at particular times during the summer of 2017, and the levels of microcystins are affected by spatial, temporal and climatic variables, such as season, temperature, and level of precipitation. Future assessments will continue to inform on the risk of exposure in different parts of the country.

References and links to other data sources

  1. Graham, J.L., Loftin, K.A., and Kamman, N. 2009. Monitoring Recreational Freshwaters. LakeLine. Vol. 29, pp. 18-24.
  2. Lopez, C.B., Jewett, E.B., Dortch, Q., Walton, B.T., and Hudnell, H.K. 2008. Scientific Assessment of Freshwater Harmful Algal Blooms. Interagency Working Group on Harmful Algal Blooms, Hypoxia and Human Health of the Joint Subcommittee on Ocean Science and Technology, Washington, DC.
  3. Hoagland, P. and Scatasta, S. 2006. The economic effects of harmful algal blooms, in Ecology of Harmful Algae, Graneli, E., Turner, J.T. (Eds.):  Ecological Studies Series.  Springer-Verlan, Heidelberg. Vol. 189, Chap. 30, pp. 391-402.
  4. Paerl, H.W. and Fulton, R.S. 2006. Ecology of harmful cyanobacteria, in Ecology of Harmful Algae, Granéli, E., Turner, J.T. (Eds.): Ecological Studies Series.  Springer-Verlan, Heidelberg. Vol. 189, Chap. 8, pp. 95-109.
  5. Chorus, I. and Bartram, J. 1999. Toxic cyanobacteria in water: a guide to their public health consequences, monitoring and management. Published on behalf of WHO by E & FN Spon/Chapman & Hall, London.
  6. U.S. EPA. National Rivers and Streams Assessment.
  7. U.S. EPA. Wadeable Streams Assessment.
  8. U.S. EPA. National Wetland Condition Assessment.
  9. National Oceanic and Atmospheric Administration. National Ocean Service - Harmful Algal Blooms: Tiny Organisms with a Toxic Punch.

Nutrient Pollution

  • Basic Information
    • Sources and Solutions
      • Agriculture
      • Stormwater
      • Wastewater
      • Fossil Fuels
      • In and Around the Home
    • The Effects
      • Human Health
      • Environmental
      • Economic
    • Where it Occurs
      • Lakes and Rivers
      • Coasts and Bays
      • Ground Water and Drinking Water
      • Air
  • What You Can Do
    • In Your Home
    • In Your Yard
    • In Your Community
    • In Your Classroom
  • The EPA’s Efforts to Reduce Nutrient Pollution
    • 2022 Nutrient Reduction Memorandum
    • Ongoing Efforts
    • Previously Issued Policies and Documents
  • Data and Tools to Assist States, Tribes, & Territories
    • Nutrient Data
    • Surface and Source Water Tools
  • Learn about Numeric Nutrient Criteria
    • Programmatic Information
    • Technical Support for Criteria Development
    • State Progress Toward Adopting Numeric Nutrient Criteria for Nitrogen and Phosphorus
  • Research, Reports, & Other Resources
    • Research and Reports
    • Technical Resources
Contact Us about Nutrient Pollution
Contact Us to ask a question, provide feedback, or report a problem.
Last updated on December 2, 2024
  • Assistance
  • Spanish
  • Arabic
  • Chinese (simplified)
  • Chinese (traditional)
  • French
  • Haitian Creole
  • Korean
  • Portuguese
  • Russian
  • Tagalog
  • Vietnamese
United States Environmental Protection Agency

Discover.

  • Accessibility Statement
  • Budget & Performance
  • Contracting
  • EPA www Web Snapshot
  • Grants
  • No FEAR Act Data
  • Plain Writing
  • Privacy
  • Privacy and Security Notice

Connect.

  • Data
  • Inspector General
  • Jobs
  • Newsroom
  • Regulations.gov
  • Subscribe
  • USA.gov
  • White House

Ask.

  • Contact EPA
  • EPA Disclaimers
  • Hotlines
  • FOIA Requests
  • Frequent Questions
  • Site Feedback

Follow.