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On August 20, Washington County Parks identified blue green algae in Point Douglas Beach and St. Croix Bluff Beach, two popular swimming locations for Hastings residents. While blue green algae is nothing new in the area, it can still pose a threat to people and especially their pets. Blue Green algae can release a number of toxins most common of which is Mycrocystin which is known to cause rashes and blisters if exposed to skin, and nausea, numbness in extremities and diarrhea among other symptoms if ingested. While most people will recover from these symptoms within 72 hours, exposure to blue green algae can be fatal to dogs.

The Basics

Blue green algae is a pretty misleading name for a substance that is not algae, and isn’t aways blue or green. What people mean when they say blue green algae is Cyanobacteria, a type of bacteria named for its cyan hue. While classified as bacteria, Cyanobacteria acts like algae in that it can use photosynthesis.

Based on research from the Lilly Center for Lakes and Streams in Winona Lake Indiana, records of Cyanobacteria date back to the 1920s indicating that they aren’t invasive but that their massive blooms could be a factor of changes in the environment including fertilizer runoff.

Blooms and Toxins

The term ‘bloom’ refers to a massive growth of Cyanobacteria that can cover the surface of water turning it green or blue-green. Cyanobacteria naturally contain toxins within their cells which can be harmful to humans and especially dogs. Cyanobacteria release these toxins gradually over time but when blooms die off, the cells break and can release massive amounts of toxins into the water making it dangerous to swim in.

As to exactly why Cyanobacteria release toxins, “That’s what we are trying to figure out, so we don’t have a lot of detail,” said Nathan Bosch, Director of the Lilly Center for Lakes and Streams. Several theories include releasing toxins as a competitive response, as a defense mechanism against zooplankton, and as a chemical queue from the environment.

Despite not believed to be an invasive species, Cyanobacteria are consistently able to out-compete other organisms and dominate local ecosystems in large blooms. Part of their success has to do with Cyanobacteria being able to control their own buoyancy which allows them to elevate to the surface of the water in order to photosynthesize, sink deeper into the water to avoid DNA damage due to solar radiation, as well as dive to the bottom of bodies of water in order to gather nutrients. Cyanobacteria are actually able to gather more nutrients than they need in a process called luxury uptake which allows them to both pull more nutrients from their environment and then grow extremely quickly afterword.

Finally, Cyanobacteria get help from invasive species. Zebra mussels eat many native organisms but not Cyanobacteria, instead spitting them out. “What you are left with is more of these toxins,” said Bosch.

Identifying Blue Green Algae

Identifying a Cyanobacteria bloom instead of other plants and algae like duckweed or green algae can be difficult which is why the Minnesota Department of Natural Resources (DNR) recommends several tests for identifying blue green algae versus other native organisms.

The first and easiest test is the stick test. Find a sturdy stick and dip it into the water. If the stick comes out “looking like it has been dipped into a can of paint, the material is likely blue green algae. If the stick comes out with green strands like hair or threads, the material is probably filamentous green algae, which may be a nuisance but is not a health hazard,” according to the DNR.

Other tests include putting lake water filled with algae into a jar and refrigerating it overnight. In the morning, if the algae have settled to the bottom of the jar, it is likely not blue green algae. If instead the algae have formed a ring at the top of the waterline, the water is likely to contain blue green algae.

What to do about Blue Green Algae

Bosch is quick to note that “just because there’s algae doesn’t mean there is a lot of toxins in the water.” Some blooms do not release large amounts of toxins which is why scientists are actively studying the phenomenon.

Cyanobacteria varies lake to lake and even within large bodies of water. “Sampling within a single lake can be very different,” due to various factors including prevailing wind direction, water depth and clarity said Bosch. Just because one lake has a large bloom doesn’t mean others around it will too, unless they are hydrologically connected.

What you shouldn’t do is dump algicide into the body of water. In killing the Cyanobacteria, the cells will break open and release more toxins into the environment.

In the meantime, consider other locations in which to swim, especially if you are bringing furry friends along.