Blue green algae on beachBlue-green algae, also known as cyanobacteria, is harmful to people and pets. Before getting in the water, always take an overall look at water conditions and do not enter the water if you see blue-green algae. Water conditions can change quickly, and posted water quality signs may not always reflect real-time conditions.


Spotting a Blue-Green Algae Bloom

Despite its name, blue-green algae may not always be blue-green. It may also be reddish-purple or brown. Blue-green algae causes the water to be murky. See photos of blue-green algae.

When environmental conditions are just right, blue-green algae can grow very quickly. Most species are buoyant and will float to the surface, where they form scum layers or floating mats.

  • Do not swim in water that looks like "pea soup", green or blue paint, or that has a scum layer or puffy blobs floating on the surface.
  • Do not boat, kayak, or water ski in water with blue-green algae (you can be exposed to the toxins through breathing).
  • Do not let children play with scum layers, even from shore.
  • Do not let pets or livestock swim in or drink water with blue-green algae blooms.
  • Do not treat water that has blue-green algae blooms with any herbicide or algaecide - toxins are released into the water when blue-green algae cells die.

If You Have Been in the Water with Blue-Green Algae

  • Rinse off well when you get out.
  • If you have symptoms you think are due to contact with blue-green algae, call your health care provider or Poison Control Center at 1-800-222-1222.
  • Report a blue-green algae bloom or illness to the Wisconsin Harmful Algal Blooms Program (WI DHS).

Tips for Dog Owners

Dogs that come into contact with blue-green algae blooms can get sick, and sometimes die because their bodies are smaller and they tend to swallow a lot of water.

  • Always look at water conditions before letting your dog swim or wade.
  • Give your dog fresh water to minimize the amount of lake water they drink.
  • Rinse your dog off as soon as possible after being in the water. Since dogs often lick their fur, they can swallow toxins even after they are dry.

If your dog has been in the water near a blue-green algae bloom and they seem sick, call your vet.


Reducing Frequency and Intensity of Blue-Green Algae Blooms

There are no quick and easy fix once blue-green algae appears in a lake or pond. Reducing the amount of nutrients that wash into our lakes and ponds will eventually reduce the frequency and intensity of blue-green algae blooms, but it may take a long time and a lot of community involvement to effectively change the nutrient concentrations in a water body.

You can help reduce nutrient concentrations by:

  • Minimizing the use of lawn fertilizers.
  • Not using phosphate-containing fertilizers.
  • Performing routine maintenance on your septic system.
  • Preventing leaves and grass clippings from washing into storm drains.
  • Maintaining native vegetation along shorelines as buffer areas to help filter run-off.