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Fluorescent green water, choked with algae. Scarce wildlife. Little to no vegetation.
Since 1909, Freeborn Lake in southern Minnesota was struggling to survive. That was the year the outlet of this 2,222-acre shallow lake was dammed to control flooding, prevent drought-like conditions in the lake and promote farming downstream.
The dam succeeded in holding water and supporting new agriculture, but an unintended consequence was a less resilient lake with water levels unable to naturally fluctuate with wet and dry seasons. After invasive common carp took over, plants died were destroyed and water quality diminished.
“This is a classic prairie shallow lake that should have a mix of emergent vegetation and submergent vegetation and aquatic invertebrates,” said John Lindstrom, Ducks Unlimited biologist in Minnesota. “Vegetation is the basis for clean water. Without it, what we had was water the color of green pea soup.”
Freeborn County leaders turned to Ducks Unlimited for a solution and for the first time in more than 100 years, the lake is becoming a clean, healthy body of water for ducks and residents.
Crucial to wildlife, waterfowl
Jeanine Vorland, area wildlife manager for the Minnesota Department of Natural Resources Owatonna Area, said the lake plays a big role in large-scale habitat conservation efforts.
“These large shallow lakes provide an important habitat component that you don’t find in a smaller basin,” she said. “Because of its size and location, it’s pretty critical.”
According to the Minnesota DNR, the lake has been an important migratory stop for waterfowl and other waterbirds. Coots and other waterfowl, including mallards and diving ducks, are common in spring and fall migration, but numbers are limited by the lack of food in the lake. At least 20 species of greatest conservation need use shallow lake habitats throughout Minnesota.
Tied to the community
Freeborn Lake has about 16 miles of shoreline with a mixture of residential areas, farmland, park and conservation lands, forests, wetlands, public rights-of-way and a golf course.
The lake has a strong hunting heritage, but one that has suffered throughout the years as water quality decreased.
“The lake has a history of being an important resource for hunting and fishing,” Vorland said. “But from a local standpoint, it’s been an impaired resource.”
The wet-dry cycle is crucial to the health of shallow lakes and wetlands. Because of the dam, the only time the water levels significantly decreased was during strong periods of drought. The last prolonged dry spell was during the 1970s, meaning it’s been about 40 years since the lake has had a chance to rid itself of contaminants.
Natural fish winterkill events also have been rare for decades, allowing invasive common carp to flourish in the lake and annually invade from the Cobb River downstream.
“It’s been almost a generation since the last drought,” Vorland said. “Some residents have been born and lived their lives since there has been clear water in that lake.”
Freeborn County and the Minnesota DNR approached Ducks Unlimited for help in 2014.
“It presented some challenges,” said Jim James Streifel, Ducks Unlimited’s manager of engineering services and lead engineer on the project.
The answer was replacing the aging, failing dam with a modern water-control structure. The new structure differs from a dam in that it enables the Minnesota DNR to manage lake levels. By adding or removing boards, Vorland and her team can replicate the natural flooding and drying of the shallow lake. Those cycles encourage vegetation growth while killing off invasive fish during the winter months.
Streifel and his engineering staff had to consider a multitude of factors when designing the structure. The design also includes a fish barrier, which prevents invasive fish from entering the lake, destroying vegetation and resuspending bottom nutrients.
Construction was completed in December, and the lake is now in a state of draw-down. The DNR has opened the new structure, which has drained a majority of the water. The remaining water will freeze this winter. Next spring and summer, the exposed lakebeds will compact, germinating the seeds of generations of plants.
“We do expect to see an increase in vegetation next year,” Vorland said. “But if all goes as well, water will be fully restored in growing season of 2019 and we’ll have clean water for the first time in a generation.”
The project was funded in large part through a 2014 Minnesota state appropriation from Minnesota’s Outdoor Heritage Fund as recommended by the Lessard-Sams Outdoor Heritage Council. Also funding the project are Freeborn County and a grant recently recommended by the North American Wetlands Conservation Council.