RICE -- Jeff Soderholm's family has spent 42 years in a cabin on the north side of Little Rock Lake, but it's no longer the mecca of fishing and water sports he remembers.
Each June for the past two years, heavy mats of weeds floated along the surface. By mid-summer, the plants died off and were replaced by a scum of green algae that coats the water's surface.
"By the Fourth of July, it was like pea soup," Soderholm said.
The culprit doesn't grab headlines the way Eurasian milfoil has for the past decade as a major threat to the health of Minnesota's lakes. But experts say curly-leaf pondweed is more common, just as much of a nuisance and perhaps even more difficult to control than its better-known counterpart.
"It's becoming probably one of the most invasive aquatic species we have in Minnesota right now," said Paula West, executive director of the Minnesota Lakes Association.
Like milfoil, curly-leaf pondweed can be transported from lake to lake by careless boaters who don't clean the weeds off their motors. Once it's in a lake, it spreads quickly and is extremely costly to control.
The nuisance plant is causing serious headaches for the state Department of Natural Resources, lake associations and concerned lakeshore owners such as Soderholm who want to find a way to get rid of it.
Soderholm helped create the Little Rock Lake Clean Water Committee, which he hopes will find a solution by asking experts for advice and developing a plan of attack.
If nothing is done, Soderholm fears the lake's quality will continue to deteriorate. Already, his cousins don't come to the cabin to swim anymore. During last fall's duck-hunting season, he had to scrape scum from his decoys.
"The way we look at it, it's something that could destroy the lake," Soderholm said.
Threat to lakes
Curly-leaf pondweed has been in Minnesota at least since the early 1900s. Since then, it has spread to more than 500 lakes, including Little Rock and Mayhew lakes in Benton County and parts of the Sauk River Chain of Lakes in Stearns County.
"It's in almost every county in the state," said Neil Vanderbosch, DNR aquatic plant management specialist.
Curly-leaf's unusual life cycle gives it a competitive edge over other aquatic plants. It sprouts from seedlike pods called turions in the fall and continues to grow under the ice during the winter. Typically it's the first plant to bloom in the spring and dies off by late June or early July.
While in bloom, curly-leaf pondweed grows quickly and can create a mat of vegetation near the surface. It clogs up boat motors and makes the lake unappealing for swimming and other water sports.
"It's a problem that is getting really bad," said Don Zieglmeier, president of the Little Rock Lake Association. "People are getting really uptight. It's so bad now, in some places you can't go 40 feet without cleaning off your (propeller)."
Recent winters marked by late freezes, minimal snow cover and early melts have been ideal for curly-leaf, said Steve McComas of Blue Water Science, a St. Paul-based consulting firm that helps lakes battle the plant.
"The last few years have been perfect growing years, so that's why it's become more noticeable," McComas said.
Once curly-leaf pondweed takes over in a lake, it can shut out other native vegetation, Vanderbosch said.
"It can cause huge water-quality issues," he said. "In some lakes, it's the only plant in the lake now."
Even after the plant dies, the problems continue. The rotting vegetation consumes oxygen, which can affect fish habitat, said Mark Hauck, Benton County Soil and Water Conservation District manager.
It also releases nitrogen and phosphorus, two nutrients that fuel algae growth, Hauck said. Little Rock Lake is seeing a growth spurt of blue-green algae, a stinky scum that can be a skin irritant for humans and a health hazard for animals that ingest it.
"It's just smelly and very unsightly," Hauck said.
Search for solutions
There is no cheap or easy way to control curly-leaf pondweed. In Sauk Lake near Sauk Centre, a weed harvester has been battling the plants for almost 15 years, but it's an imperfect solution, said Julie Klocker, administrator of the Sauk River Watershed District.
"That's more like mowing the lawn than actually taking care of the problem," she said.
The watershed district is looking into other potential solutions, such as drawing down the lake's water level during winter months to expose the turions or chemically treating the plants with an herbicide.
The DNR strictly regulates who can apply such chemicals and in what amounts, typically limiting application to small areas. But the DNR has been experimenting with allowing variances to treat large portions of a lake to see if curly-leaf pondweed can be eradicated, Vanderbosch said. That approach met with some success in Medicine Lake near Plymouth, he said.
Still, such chemical treatments are costly ‹ as much as $300 an acre, West said. And because curly-leaf pondweed can keep coming back, several years of treatment are needed.
"Most of these lake associations just don't have the money to do that," she said.
For a lake such as Little Rock, which spans 1,270 acres, that's a hefty price tag. And while the DNR offers funding for treating lakes with Eurasian milfoil, there is no money available for controlling curly-leaf pond-weed.
"In our opinion, the DNR needs to take a more aggressive approach to curly-leaf management," West said.
Do your part
Ways to prevent the spread of exotic species:
- Inspect your boat, trailer and boating equipment. Remove any visible plants and animals before leaving a lake or river.
- Drain water from the motor, livewell, bilge and transom wells while on land.
- Dispose of any unwanted bait in the trash. Never release live bait into a lake or river or release aquatic animals from one lake into another.
- After returning home, wash and then dry your boat, tackle, trailer and other equipment with hot tap water or a high-pressure sprayer to kill harmful species that weren't visible at the boat launch. Or let dry for at least five days before transporting to another lake or river.
- Learn what exotic species look like and report any new infestations. See the Department of Natural Resources' Web site at www.dnr.state.mn.us.