Madison is seeing earlier algae blooms than typical — Public Health Madison & Dane County closed Spring Harbor Beach on Wednesday due to a large blue-green algae bloom in the water — signaling the toll climate change is taking on the city’s lakes.
Blue-green algae is formed by cyanobacteria, a toxin that can cause stomach upset, rashes and respiratory irritation, as well as have deadly effects on dogs.
A combination of warm temperatures, sunlight and nutrient-rich waters can cause blue-green algae to reproduce rapidly, or bloom. Within a few days, a clear lake can become cloudy with algae growth.
“This definitely is early in the season, (especially) for such a significant bloom,” said Jennifer Lavender-Braun, a microbiologist for Public Health Madison & Dane County. “The general consensus from concerned citizens, as well as scientists in the field, is that we're going to see more of this due to climate change, and (see) the impact of that on our lakes.”
While algae blooms can vary in appearance, the Spring Harbor Beach bloom on Lake Mendota looks like spilled turquoise paint on the water with white scum floating on top, Lavender-Braun said. Public Health department lab staff are just beginning their annual water quality monitoring at local beaches, which goes from Memorial Day through Labor Day.
During the summer, the department tests lake water quality for E. coli and for blue-green algae. If a test shows concerning results, there will be signs posted at the beach and updates online notifying people to stay out of the water. (Technically all the beaches are closed until May 29.)
“Having the blooms this early in the season, it's never a sure predictor that this is going to be how it is for the rest of the summer,” Lavender-Braun said, “but it can be really hard to predict and it can change very quickly.”
She recommended that residents visiting beaches always check PHMDC’s website and the water before diving in. Beachgoers can sign up for beach condition alerts. If you notice anything concerning, you should report it to the department, Lavender-Braun said.
“We really appreciate when people do report it to us at Public Health so that we can respond,” she said, adding that the department monitors 23 beaches throughout the county. “We cover a lot of lakes and a lot of ground and we can't be everywhere at once.”
Grace Wilkinson is an assistant professor at the University of Wisconsin-Madison’s Center for Limnology who studies how lakes are influenced by their connections to their surrounding landscapes. She said typically in the spring, she expects to see a different form of algae called diatoms in the lake because of the colder water. When that gets eaten up by zooplankton, lakes go through a clear water phase, usually in June, and then cyanobacteria pop up in July and August.
“That's the normal seasonal progression that we would expect, and so having a cyanobacteria bloom of this magnitude, that's this scummy this early in the season is not a particularly common thing that happens,” Wilkinson said. “It says a lot about what a weird spring we've been having.”
With more late season snow and then several really hot days early in the spring, the moisture and heat caused the cyanobacteria in Lake Mendota to thrive. Wilkinson believes it is an indicator of what’s to come in the years ahead with warming temperatures and atypical shoulder seasons — spring and fall.
On top of that, invasive species like spiny waterflea and zebra mussels are “really messing with how algae is growing and really changing the way that the lake is functioning,” Wilkinson said.
“We're starting to see that interaction between climate and other species changes within the lake, and that, perhaps, might be what's causing these earlier blooms. There's lots of folks here at the university that are working on answering that question.”
Often called “the most studied lake in the world,” Lake Mendota has been studied for over 100 years, which Wilkinson said is a “huge benefit.”
“We're well positioned to know this is outside the normal and try to figure out why it's happening so that we can hopefully provide some more tools or some more ideas about how we can manage this and protect people,” Wilkinson said.
Should residents discover they are in the water near a bloom, it is important to avoid swallowing water and rinse off well afterward. Dogs that have been in water near a bloom should also be rinsed well and see a vet if they seem ill.
