Yahara Portal

Explore the legacy and future of the Yahara Lakes and Watershed

What is blue-green algae?

If you have ever looked at a lake that appeared to have had a can of turquoise paint thrown on it, it’s is very likely that you have seen a blue-green algae bloom. The Yahara Lakes are known for summer blue-green algae blooms. What’s the difference between blue-green and green algae and why is it important?

There are lots of different kinds of algae and some play a healthy role in a lake environment while others don’t; blue-green blooms fall into the second group. The word cyan, a turquoise blue-color, combined with the word bacteria, makes cyanobacteria, another term for blue-green algae. Surprisingly, blue-green algae can also be green, blue, reddish brown and brown.

Blue-green algae are really a type of bacteria that photosynthesize, a process by which plants produce their own food by using sunlight and carbon dioxide and release oxygen. Blue-green algae have a lot of characteristics that differentiate them from green algae. Unfortunately, some of these special characteristics make them dangerous and can cause illness and potentially death in humans and animals.

When temperatures are hot in the summer and there is little wind, blue-green algae can bloom and cluster into large patches, particularly in warm and shallow water. Since one of their special characteristics is that they are buoyant (can float), they accumulate on the surface and form big mats. These are usually unsightly and smell bad.

Toxins in Blue-Green Algae

Blue-green algae have the ability to ability to product toxins, or poisons. This is one reason why they are largely inedible to fish and algae-eating microorganisms called zooplankton.

Toxins can affect fish, waterfowl and aquatic life. Toxins can affect pets and people, too. Dogs in Wisconsin have died from swimming in lakes with blue-green algae. The toxins can affect the central nervous system and cause seizures, paralysis, respiratory failure and death.

The algae can also cause other types of allergic reactions in the eye, throat, nose and skin. Other problems include vomiting or diarrhea. These symptoms can present themselves between several hours to several days after being exposed.

Public beaches on the Yahara lakes are sometimes closed in the summer due to blue-green algae blooms. Heed these signs and don’t swim there.

Beware of water that looks like paint or pea soup—don’t swim or even wade in these waters and keep your pets away. Take other precautions like showering with soap after swimming in the lakes and wash your hands after coming in contact with potentially affected water.

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