City Cast

🌊 The Muck in Our Lakes

Hayley Sperling
Hayley Sperling
Posted on August 16   |   Updated on September 12
Blue-green algae is a type of bacteria that grows toxic blooms in our lakes. (Photo by City of Madison)

Blue-green algae is a type of bacteria that grows toxic blooms in our lakes. (Photo by City of Madison)

Being on an isthmus, Madisonians are surrounded by water. But unfortunately, because of the literally freezing-cold winters and other environmental factors, our time on the water is limited. This time of year, one of the biggest threats to our beaches is blue-green algae.

What Is It?

Despite its name, blue-green algae is a type of bacteria. It can grow quickly forming “blooms” full of toxins that can be harmful to people and animals. In humans, symptoms can include stomach upset, rashes, and respiratory irritation.

Blue-green algae may not always be blue-green. Sometimes blooms appear as reddish-purple or brown. Oftentimes, blue-green algae will look like spilled paint on top of the water.

Why Is It Here?

Blue-green algae thrives in warm, nutrient-rich water. In the case of Madison’s lakes, phosphorus runoff from fertilizer has contributed to the growth (and stench) of algal blooms.

The Madison Metropolitan Sewerage District is tasked with cleaning up the phosphorus in our city’s water but it’s not a simple job.

How To Avoid It.

Public Health Madison and Dane County tests the waters at Madison’s beaches from Memorial Day to Labor Day and lists the open status of Madison beaches on its website.

And in general, always look at the water around you before you get in and don’t swim in water that looks like "pea soup." Don’t let your pets swim in it either.

If you see a blue-green algae bloom, PHMDC wants to hear from you.

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