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SOUTH DAKOTA Department of
Agriculture & Natural Resources

Protecting South Dakota's Tomorrow...Today!
Joe Foss Building
523 E Capitol Ave
Pierre, SD 57501-3182
Contact Us  Field Offices

Watershed Protection

Harmful Algal Blooms (HABs)

A harmful algal bloom occurs when toxin producing algae grow excessively in a body of water. In South Dakota, HABs are typically produced by blue-green algae, a primitive photosynthetic algae also known as cyanobacteria. Blue-green algae are capable of producing toxins that can be harmful to people and fatal to pets and livestock. In South Dakota, harmful algal blooms typically occur during the warm summer months in nutrient enriched lakes and ponds.

South Dakota Harmful Algal Blooms Interactive Map

To see reports of algal blooms and results of HABs monitoring in South Dakota, browse the South Dakota Harmful Algal Blooms Interactive Map. Be aware that this map does not show current conditions of toxin producing algae or algal toxins (cyanotoxins) in the state and should not be used to determine whether waters are safe for recreation at the current moment. Reports of harmful algal blooms are indicated on the map with red symbols. New reports will be added as they are received from the public or other entities. The map also presents the sample results of 2019 toxin producing algae monitoring. In 2020, monitoring for algal toxins and toxin producing algae are occurring as part of the Statewide Lake Assessment and other DENR projects. Results will be added to the map as the data is available in the winter of 2020-2021. To see the results of chlorophyll-a testing, visit the DENR Water Quality Monitoring Access Portal and search for or click on your waterbody of interest.

What should I do if I see an algal bloom?

If you witness what you believe may be a harmful algal bloom, the first, and most important action you can take is to protect people, pets and livestock by ensuring they stay out of the water. When in doubt, stay out! It is impossible to tell if an algal bloom is producing toxins without testing for toxins, so the safest course of action is to exercise caution. If you would like to contact DENR to report a potential harmful algal bloom, email or phone 1-800-438-3367.

Technical assistance is available for lake associations and other local groups wishing to test their waterbody to assess the risk from HABs. If your lake association or group wishes to recieve technical assistance for HABs, contact the DENR Watershed Protection program using the contact information listed above.

What should I do if I'm exposed to a harmful algal bloom?

If a person or animal comes into contact with HABs impacted water, take the following actions to protect yourself, your children, your pets, or your livestock:

To learn more about harmful algal blooms in South Dakota and see pictures of algal blooms, scroll through our HABs storymap below or view it in fullscreen here.


HABs Information and Links

SD DENR Blue-Green Algae Informational Brochure (pdf)

SD DENR Harmful Algal Bloom Response Protocol (pdf)

South Dakota Department of Health Algal Toxin Page

Centers for Disease Control: Harmful Algal Bloom Associated Illness

EPA: HABs page

EPA Fact Sheet: Recommended Human Health Recreational Ambient Water Quality Criteria or Swimming Advisories for Microcystins and Cylindrospermopsin (pdf)

EPA: HABs Infographic

EPA: Learn about Cyanobacteria and Cyanotoxins

EPA: Health Effects from Cyanotoxins

World Health Organization: Algae and Cyanobacteria in Fresh Water


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