Blue-Green Algae and Beach Closures: What To Know

MADISON, WI—When it comes to blue-green algae, beachgoers should know how to spot it and consult public advisories before taking a swim.

Currently, there are advisories on beaches, including BB Clarke, Frost Woods, Fireman’s Park in Verona, Warner and Hudson Park Lake Access Point. Within the city, toxin levels produced by blue-green algae are monitored weekly by Public Health Madison and Dane County.

While blue-green algae is not new to Madison’s lakes, now that summer is here and crowds are flocking to beaches, visitors should monitor advisories and know how to spot the toxin-producing plant themselves.

Gina LaLiberte, the Statewide Harmful Algal Bloom Coordinator at the Wisconsin Department of Natural Resources, discussed what to know when it comes to blue-green algae.

The conversation has been edited for clarity.

The basic rundown: what is blue-green algae?
Scientifically known as cyanobacteria, blue green-algae are essentially tiny plants which are found in every body of water. The free-floating pieces that are seen on the shores are called planktonic. Unlike much of the other algae and plants you might spot in the lakes, blue-green algae can produce toxins that may cause issues if it’s inhaled, exposed to skin and but mostly if it is ingested.

“One thing that's important is that blue green algae, not all of them make toxins and not all of them make them all the time,” LaLiberte said. “But it's still really important to treat them with caution and to do your best to to not swallow water that could have either blue-green algae or other pathogens in it. There's always other things like bacteria and viruses and other parasites in untreated surface water that could make you sick if you swallow it.”

How can you spot it?
Blue-green algae can look like tiny little particles or green dust in the water.

Those thick mats of algae that float near the shore and look like slippery “green hair” are known as filamentous green algae. While these are mushy and not ideal for swimming, they do not produce toxins. Another nontoxic plant, duckweed, is also green but has little roots which can distinguish it from blue-green algae.

What are best practices?

Since blue-green algae float, they can get pushed around quickly and frequently by the wind. This is one of the reasons why it is important to monitor the water yourself since blooms at one beach can travel across the lake to another.

Outside of Dane County, other Wisconsin lakes may not be monitored on such a regular basis. It is best to follow beach advisories when they are available, but also check out the water for yourself and be sure that kids and pets are never ingesting surface water. Besides blue-green algae, this water can house other bacteria and parasites.

“One thing that's useful is to pay attention to the wind direction as well,” LaLiberte said. “ If you know that the wind has been coming out of a particular direction for a few days, you may find better swimming conditions if you go to the upwind direction on the lake.”

How do humans affect these conditions?
Like any plant, blue-green algae need nutrients to grow and reach high numbers in our lakes. Things like fertilizer, grass cuttings and leaves can run off into lakes, serving as a major nutrient source. Madison residents should try to minimize fertilizer use and keep any sort of yard waste from ending up in the gutter.

“People really need to be cognizant of how their actions are affecting what happens in the water downstream from them,” LaLiberte said.