All five Yahara lakes saw cyanobacteria (blue-green algae) blooms throughout the summer of 2019. One bloom in particular on Lake Mendota was quite large, covering at least an area from Picnic Point to the Memorial Union on August 1st. The bloom was well-documented by photos from community members as having a green pea soup-like consistency.
Cyanobacteria blooms are often bright green, but can also appear in shades of brown, blue, and white. Typically, blooms are spotted on warm days with calm winds. On August 1st, Madison reported a high of 81 degrees with an average wind speed of two miles per hour.
So what is it? Cyanobacteria are unicellular microscopic organisms. They have existed on earth for more than two billion years, with more than 2,700 types of the bacteria documented. The photosynthetic bacteria convert sunlight into energy and can regulate their buoyancy to create floating scums. Cyanobacteria blooms can last for hours on our lakes, or persist for days.
Learn more about cyanobacteria here!
It may seem odd, but this shoreline foam is a natural side effect of decomposing aquatic plants. Many dissolved organic compounds released from decaying plants are surfactants, which means they reduce the surface tension of liquid, similar to the soap we use every day. These surfactants allow air to mix and form mats of foamy bubbles. It is important to note that the presence of foam is unrelated to cyanobacteria blooms, but the two phenomena can occur at the same time.
What’s with the blooms?
Cyanobacteria blooms may be jump-started when rain washes nutrient-rich agricultural and urban waste into our lakes. At Clean Lakes Alliance, we’re working to reduce phosphorus runoff into our lakes so we have more days where our lakes and beaches are open, enjoyable, and safe.
Cyanobacteria can produce toxins that make people and animals sick. Do not swim in areas where cyanobacteria are forming visible blooms. One pound of phosphorus entering our lakes can produce up to 500 pounds of algae! Do your part to keep our lakes clean.