Blue-Green Algae

What are cyanobacteria or blue-green algae?

Blue-Green Algae/Cyanobacteria are aquatic organisms that are found as floating mats on the surface of lakes or ponds. There are health concerns associated with contact Blue Green Algae and the toxins produced by some species. 

Does the presence of an algae bloom always mean the water is contaminated?

No. Just as not all cyanobacteria have blooms that are visible, not all cyanobacteria produce harmful toxins. Between 30 and 50 percent of blooms are from non-toxic species of cyanobacteria. 

What should I do if I see a bloom?

People should use common sense when dealing with algae. It is impossible to tell from a visual inspection whether an algal bloom is toxic. The safest thing to do is to treat every algal bloom as if it could be dangerous.

Guidance for people:
  • Do not swim or wade through algal scums.
  • Do not boat, water ski, or jet ski through algal blooms.
  • Do not fish in lakes where algal scum is present.
  • Always shower off with soap and water after swimming in a lake.
Guidance for pets:
  • Do not let dogs drink lake water during an algal bloom.
  • Do not let dogs eat algal scum, or lick it off their fur.
  • Wash your dog off with clean water immediately if your dog swims or wades in water during an algal bloom. 
What to do if exposed:
  • Immediately shower off with fresh, clean water.
  • Monitor for sudden signs of blue-green algae-related illness, such as: Vomiting, Diarrhea, Headache, Abdominal pain, Cough, Sore throat, Skin rash, or Blistering.
  • Seek medical care if symptoms occur or call the Wisconsin Poison Center at 800-222-1222 for advice. If pets become suddenly ill with signs of poisoning, bring them to a veterinarian immediately.
  • Report blue-green algae-related illnesses to your local health department. They can track exposures, and use this information to determine when sampling efforts need to be increased, or if water bodies should be closed to the public.
Additional Resources