Big Round Lake

Sampling aquatic plants on Big Round Lake.

‘We can turn ‘em around’


If a lake is coated with algae, it is probably best to avoid taking a dip in it, for reasons beyond that it is gross and slimy. 

So as summer heats up, what do area swimmers need to know?

Well, most lakes in the Osceola area are eutrophic, according to Polk County Water Quality Specialist and Aquatic Invasive Species Biologist Jeremy Williamson. For context on what this means: a body of water’s trophic state index is a measurement of the nutrition content it contains, as well as its productivity, the amount of water used in order to yield a certain quantity of product. 

Oligotrophic waters are low in nutrition and productivity, with very little algae. Such waters are clear and good for drinking. Mesotrophic waters are somewhat productive, nutritious and clear and support considerable levels of flora and fauna. Eutrophic waters, like most of Osceola’s lakes, are very productive and full of nutrients and plants. While the oxygen emitted from aquatic plants supports wildlife growth beneath the surface, it can also lead to the lake becoming overwhelmed with algae, harming animal life.

Williamson elaborated on what exposure to an algae-heavy lake could entail for swimmers.

“Those lakes will turn green in August, just because of how the landscape is,” Williamson said. “We have had instances where dogs have died from algae poisoning. The phone starts ringing when that happens… A productive lake is usually a productive fishery, but in August, you may not want to bring your two-year-old swimming there if there’s some pretty prolific algae bloom.”

In humans, rashes are a common response to excess algae. 

“In general, from a water quality standpoint… looking at just water health in and of itself, we’re always pushing toward lower trophic status,” Williamson said. “[Osceola lakes are quite] eutrophic. They have high nutrients, they have quite a bit of algae, that said, we can turn ‘em around.”

One action taken to improve water quality in regard to algae levels is the application of aluminum sulfate (alum) to Cedar Lake, approved at the Cedar Lake Protection & Rehabilitation District annual meeting and funded by property taxes and a DNR grant. Alum application dispels the phosphorus that fuels algae growth, clearing and oxygenating waters. Excess phosphorus spreads from lake to lake, as Horse Lake flows into Horse Creek, which flows into Cedar Lake.

Additionally, “within the watershed… we have this fantastic group of agriculture producers, who are doing this fantastic work with no-till scenarios,” Williamson said.

“They’re not tilling the soil, they’re planting right into last year’s crop residue. All the microbiology in the soil isn’t getting worked up and broken up and destroyed, and we’re seeing incredible results based off of that. We’re seeing very little nutrient leaving the field.”

Carp, an invasive fish species, poses another dilemma.

“We have some unique challenges. Lotus and Horse (Lakes), and Cedar to a certain extent, are really infested with carp. Carp are a problem, they root up the bottom,” Williamson said. “Even if you have a lake that’s high nutrient — for example, if you have a really nice plant community, it still might be super clear. But then you add carp, and that vegetation ceases to exist.”

He illuminated the balance necessary for a prosperous lake.

“Cedar Lake has a great walleye fishery, because it’s so productive, so how do you define quality? Is it because you want to fish? Do you want to swim?” he said. “The goal is to have [a lake] function biologically, so that you have a healthy plant community, a healthy fish community, and it’s not hazardous to people to go swimming.”

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