Blue-green algae are not algae at all, but rather types of bacteria called cyanobacteria. Cyanobacteria thrives when there is a combination of two factors: warm weather and nutrient-dense water. Some variations of cyanobacteria produce toxins and cause cause severe illness in humans and pets.
It is important to remember that algae blooms are a normal part of lake ecology and most blooms are not harmful. There is no way to tell if a blue-green algal bloom is harmful just by looking at it.
How can you spot blue-green algae?
Water that contains algae blooms will take on the appearance of pea-green paint or may slime on the surface. If certain wind conditions are present, the film will concentrate on shoreline areas where animals may drink or swim.
Can you prevent harmful blooms?
We cannot control the weather, but we can reduce the amount of nutrients introduced into the water through run-off. Use zero-phosphorus fertilizers on your lawn or garden. Look for “0” in the middle number of the N-P-K (Nitrogen-Phosphorus-Potassium) ratio. Keep leaves and grass clippings off streets and storm drains. And plant deep rooted native plants along shorelines. Learn more about Lake-Friendly Landscaping
How can you test for blue-green algae?
A couple of simple, no cost tests can help you determine if blue-green algae is present using a jar or a stick. Learn how to test here.
If blue-green algae is present who should you contact?
You can contact the Minnesota Pollution Control Agency at (651) 296-6300 or 800-657-3864 info.pca@state.mn.us with questions about blue-green algae or the results of your test. Alternatively, if you observe a large or very dense bloom you can report using the bloomWatch app.
When in Doubt, Stay Out
Because you cannot tell by looking at blue-green algae whether it is toxic or not, it is best to avoid swimming or otherwise recreating in areas with algal blooms. If you or your pet are exposed to an algal bloom, be sure sure to rinse off with fresh water immediately.
For more information about possible health effects and the risk levels of different recreational activities, visit the MN Pollution Control Agency Blue Green Algae Information Page and the MPCA Blue Green Algae Response Flyer. Additional resources may be found at the MN Department of Health website. Check the status of monitored swim beaches here.
Other Common Types of Algae
- Bryozoans – View MN DNR webpage
- Algal Blooms, Scums, and Mats in Ponds including Filamentous- View University of Arkansas