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 toxin producing algae monitoring. Monitoring for algal toxins and toxin producing algae is conducted as part of the Statewide Lake Assessment and other DANR projects. Results will be added to the map as the data is available. To see the results of chlorophyll-a testing, visit the DANR 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 DANR to report a potential harmful algal bloom, email DANRMail@state.sd.us or phone 605-773-3623.

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:

  • See a doctor if a person is exposed or see a veterinarian if an animal is exposed
  • Shower immediately
  • Contact your poison control center for advice


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.