MADISON, Wis. - A recent bloom of cyanobacteria closed Lake Mendota swim access from Memorial Union and continues to cause concern for officials.
Cyanobacteria, commonly known as blue-green algae, forms in lakes after a combination of high heat, little to no wind and excess nutrients, such as phosphorus. When clumps of the bacteria form together it creates what is called blooms. While not all blooms contain species of cyanobacteria that are toxic, it's possible that they do.
The University of Wisconsin Madison takes precaution in swim advisories when blue-green algae blooms are present. Ultimately, it's up to University Health Services' Environmental and Occupational Health to determine if the water is safe by testing the blue-green algae.
According to a tweet from UHS, a blue-green algae bloom began forming July 31, the same day the Wisconsin Union canceled Family Night due to "current water conditions."
A blue-green algae bloom was visually confirmed to be forming along UW Madison's shoreline; samples are being collected. In the meantime, avoid all aquatic activities at the Memorial Union Swimming Pier, Hoofers Pier, and Tong Marina T-Dock. pic.twitter.com/09rCvcZrR3— UHS UW-Madison (@UHSMadison) July 31, 2019
Wisconsin Union communications director Shauna Breneman said the Union collaborates with multiple departments to determine if weather will impact a Union activity.
"The Union reviews multiple factors in advance of events, including forecasted temperature, wind speed, wind gusts, percent chance of rain, amount of rain predicted and thunderstorm possibility," Breneman said in an email.
Cyanobacteria has been an issue since about the 1930s, according to UW limnology expert and UW integrative biology professor Emily Stanley, but it's the past five years that puts cyanobacteria at its worst for Madison-area lakes.
"This summer has just been constant, sort of steady blue-greens in the lake," Stanley said. "It's been always green. I would rank this as a high up there in the bad blue-green summers."
Stanley said one of the biggest factors of an algae bloom is the excess phosphorus in lakes, and that the majority of the phosphorus comes from nearby row crop and dairy farms. Farmers might use cow manure to fertilize their crops, and when the rain washes part of the fertilized soil away, it can end up in lakes.
"Farmers have to put [manure] somewhere. It doesn't just magically disappear," Stanley said.
Clean Lakes Alliance founder and executive director James Tye said phosphorus attaches itself to soil, which is why when the soil leaks into the lakes, the phosphorus does too.
Beyond high heat and excess phosphorus, factors such as Bythotrephes longimanus, or spiny water flea, and zebra mussels are preventing cyanobacteria clean up. The spiny water flea is an invasive predator that eats invertebrate that eat blue-green algae. Zebra mussels on the other hand will eat anything but the algae, Stanley said.
"When spiny water flea showed up, the water quality got worse," Stanley said.
There are ways, however, to help reduce the amount of cyanobacteria. Stanley suggested people clean up leaves in their yard, pick up dog and animal waste and refrain from adding phosphorus as a fertilizer to yards. She said most lawns don't even need phosphorus fertilizers.
"Build a rain garden, a rain barrel, things like that," Tye said. "Keep the water on your own land, and let that water sink down into the ground, versus pushing it through the streets and into the lakes."
Community initiatives include manure digesters that concentrate phosphorus and allow less of it to escape into the water, and organizations like Suck the Muck, which remove phosphorus before it gets to the lake.
Tye said CLA donates tens of thousands of dollars to programs that research the prevention of excess phosphorus in lakes and cyanobacteria cleanup.
For those interested in swimming, Stanley recommends swimming in the middle of the lake, where cyanobacteria is less likely to grow. CLA offers an interactive map on its website that shows which lakes are deemed safe to swim in, based on samples from the organization's volunteers.
Tye said it's important to remember that while lakes such as Mendota may be infested with cyanobacteria, that doesn't mean all Madison-area lakes are unsafe to swim in. He said swimming safety is very dependent on factors like wind and size. For example, a bigger lake that gets more wind than a smaller one, might have little to no cyanobacteria.
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