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The Shell Rock River Watershed District’s administrator on Monday discussed the district’s plans to treat Fountain Lake in the near future with an herbicide to suppress an invasive species that has been predominant on the lake in recent years. 

Andy Henschel said since the district dredged in 2018, there have been dramatic increases in water quality, and with that they are seeing a good response from submerged aquatic vegetation. 

In this case, the vegetation in question is the curly-leaf pondweed, which according to the Minnesota Department of Natural Resources, is generally the first pondweed to come up in the spring and dies back in mid-summer. It is native to Eurasia, Africa and Australia but was likely introduced when common carp were intentionally introduced into Midwest waters as a game fish in the 1880, according to the DNR. The species was likely spread through the movement of watercraft and water-related equipment and was first noted in Minnesota around 1910.   

Curly-leaf pondweed generally grows from the shore to water depths of 15 feet and can grow up to 15 feet tall. It has lasagna-shaped leaves that can form dense mats at the water’s surface, according to the University of Minnesota Extension.   

Henschel said curly-leaf pondweed tends to grow faster than the native vegetation, and he said it is estimated that one curly leaf plant, if untreated, could release one million turions, which in turn germinate and produce new plants. 

The Watershed District is working with a company called SOLitude to request a permit from the Minnesota Department of Natural Resources to treat the lake with an herbicide called Aquathol, which has a salt base and does not bioaccumulate. The treatment is typically done when the lake is between 50 and 60 degrees.

Henschel said the herbicide has been used throughout the state and has been widely used in the Detroit Lakes area. The Shell Rock River Watershed District has also used the chemical once before on a 25-acre part of Pickerel Lake. 

He said while there is still curly-leaf in Pickerel Lake, it is minimal because of the native plants. 

The goal Is to cut the mass of the invasive plant by 75% and allow the native plants to then take over in growth. 

For Fountain Lake, they are looking to treat about 60 acres. Once the treatment is applied, people would need to stay out of the lake for 24 hours afterward. 

First Ward Councilor Rachel Christensen asked if there was a risk to the wildlife or ducks in the lake from the chemical, and Henschel said from the research they have conducted, there is minimal risk. There is more of a risk to the people who are handling it or who might have skin contact. 

The Watershed District will run a statement in the Tribune ahead of the treatment with more detail about the chemical. 

Henschel said he was unsure if the DNR would require property owners on the lake to sign off for the treatment but noted that the city owns 75 to 80% of the shoreline. If they are required to get all property owners to sign off, the district will reach out to the other owners as well. 

The councilors did not express any concerns about the treatment and unofficially gave the city manager approval to sign off on the treatment if that was needed before the treatment begins. Henschel said the treatment will likely have to occur once a year for five to seven years.

He noted that a drone survey conducted by the district last summer showed thicker growth of the pondweed in areas not dredged. 

The district plans to conduct the survey every year to see if the treatments are working and if they need to adjust plans moving forward.