GREEN LAKE – Conditions are improving after blue-green algae blooms spread throughout Green Lake around Sept. 16.
The Green Lake Association warned against boating and other recreation in the harmful conditions, as exposure to blue-green algae can cause illness.
As of Sept. 24, the GLA’s Facebook page reported that it appears the algae bloom has dissipated, likely from the cooler temperatures, rain and wind over the weekend.
What causes blue-green algae blooms?
According to the GLA, the Wisconsin Department of Natural Resources listed Green Lake as an impaired body of water in 2014, meaning it doesn’t meet the optimal water quality standards of the Environmental Protection Agency’s Clean Water Act.
Blue-green algae is confirmed throughout Green Lake, as of Sept. 16.
Each year, 10 tons of phosphorous enters Green Lake, which not only fuels algae blooms, but also clouds the water, depletes oxygen in the lake and puts a strain on aquatic life.
Most of it enters the lake from runoff: this includes soil and fertilizer from farms, nutrients from livestock, yard debris and pet waste, according to GLA. Other sources include, in order of prevalence, phosphorous in the air that’s deposited by rainfall, natural input from birds and aging septic systems that can leak phosphorous into groundwater.
Phosphorous pollution lowered the amount of “dissolved oxygen” in the lake, which fish and other organisms rely on to breathe.
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What is being done to combat pollution in Green Lake?
The GLA conducted scientific studies on the issue, and one of the findings was a need for 60% phosphorous reduction, as of 2021.
They set their focus on two main intervention points — the Silver Creek estuary inlet and County K marsh inlet — while also restoring streams and empowering farmers to adjust their practices.
Blue-green algae is confirmed throughout Green Lake, as of Sept. 16.
However, phosphorous that is already in the lake can linger for up to 20 years. Using their research so far, the GLA is working on trapping, intercepting or neutralizing phosphorous with wetland capture systems and sediment inactivation technologies.
What else is threatening Green Lake’s quality?
Another way the GLA is hoping to improve water quality is by addressing and preventing aquatic invasive species: plants, animals or pathogens that spread quickly and have no natural predators.
Carp, for instance, destroy vegetation and fuel algae growth while stirring up the lake bottom. Zebra mussels and rusty crayfish are other common invasive species.
Invasive plants include purple loosestrife flowers, curly-leaf pondweed and Eurasian watermilfoil, which looks similar to the native northern watermilfoil but blocks sunlight from native species.
Proactive measures against aquatic invasive species include boat-cleaning stations at Dodge Memorial County Park and Horner’s Landing.
For more about Green Lake Association or to donate to the cause, visit greenlakeassociation.org.
Daphne Lemke is the Streetwise reporter for the Fond du Lac Reporter. Contact her at dlemke@gannett.com.
This article originally appeared on Fond du Lac Reporter: Blue-green algae conditions improve on Green Lake. Here’s what’s next