Eurasian watermilfoil seen here, usually has 12-21 leaflet pairs and the leaves become limp when out of the water.
The Eurasian watermilfoil was originally discovered on Green Lake by a lake resident whose son found a fragment on the beach. Using an identification card, the father suspected the plant was Eurasian watermilfoil and brought it to the DNR office in Spicer.
A sampling at high-use areas, public accesses and resorts, found only one rooted plant, but a thorough survey of the lake by the state's exotic species crew located two strands of Eurasian watermilfoil. In all, two acres of vegetation exists near the city of Spicer.
"The good news is we found only a few plants, and there is not a lot of plant habitat in Green Lake," said Wendy Crowell, the DNR's Eurasian Watermilfoil program coordinator.
Crowell and Bruce Gilbertson of the DNR fisheries office of Spicer both feel that since the natural characteristics of Green Lake support little native vegetation, that Eurasian milfoil will find it hard to expand in the lake. Green Lake is large (5,406 acres) and round, which means all the shores receive a lot of wave action that uproots plants. The lake also has sand, gravel, and rock on the bottom, which is not ideal for plant growth.
Still, Gilbertson conceded, "It's hard to know if these stands are limited by the soil types or if it's relatively new."
The infestation in Green Lake is the 113th in the state of Minnesota, but the first in Kandiyohi County. Sauk Lake, north of Sauk Centre, and Lake Washington and Stella Lake, south of Darwin, are the only infested lakes in Stearns and Meeker counties respectively.
The spread of milfoil
"While we don't expect that milfoil will be a huge problem in Green Lake, there are a number of other lakes in the area that have a lot of plant habitat conducive to milfoil growth," Crowell explained.
Northern watermilfoil is a native species which usually has 5-10 leaflet pairs and the leaves are rigid when out of water.
This includes Long Lake, Lake Koronis, and Rice Lake in the Paynesville area. Having Eurasian watermilfoil 20 minutes away, increases the likelihood of its spreading to other local lakes.
The plant can reproduce through stem fragmentation, states the DNR website, so a single stem can take root and form a new colony. "Fragments clinging to boats and trailers can spread the plant from lake to lake," the site continues.
While a stem can as easily travel 200 miles on a boat trailer as 20, proximity increases the volume of traffic between lakes, Crowell noted, and therefore raises the chances of its spreading.
"As each new site is infested, other bodies of water that are near that site area at greater risk," said Gilbertson.
Reducing the risk
Eurasian watermilfoil can be spread by waterfowl, but the primary means of transmission is by humans. "It's crucial that everyone check and clean their boats of any plant material when leaving the lake," said Crowell. To raise awareness, the DNR is planning to have access monitors at Green Lake during some peak usage periods in the coming months.
The DNR, though, can't afford to police the accesses all the time, which means public awareness and assistance is necessary to limit the spread of Eurasian watermilfoil.
The Rice and Koronis Lake Associations have been active in awareness campaigns about Eurasian watermilfoil for the last decade. (Eurasian watermilfoil was first discovered in Minnesota in Lake Minnetonka in 1987.) Both lakes have the DNR warning signs, plus additional signs provided by their respective lake associations.
When removing their boat from a lake, owners should remove all plants and animals from the boat and trailer. Key places to check for weeds include the anchor and propeller on the boat and the rollers and axle on the trailer. Water from the live well or transom well also should be drained before leaving a lake.
Crowell credits the public for slowing the spread of milfoil in the state by using care in removing and launching boats in lakes. At the peak, there were 15 new infestations per year in Minnesota, she noted. The number of new infestations dropped as low as five per year. So far this year, there have been eight new infestations.
Peter Jacobson, Koronis Lake Association president, said the association and area lake users have worked hard to prevent the spread of Eurasian watermilfoil, but renewed diligence is needed. "It may be a call to lake users to really pay attention to what they're doing," he said. "Maybe we've become lax. We read about it, and it was far away."
Now it's in our backyard.
Matt Billo, the president of the Rice Lake Association, knows firsthand what a nuisance that Eurasian watermilfoil can be. He lived on Lake Independence, which has milfoil, and served on their lake association.
"It's not something you want," he explained. "It grows two or three inches a day. It grows to the surface and then grows sideways."
Depending on water clarity, the weeds can grow in 20 feet of water. On Rice, which has an average depth of 15 feet, that means the weed could potentially grow in half or more of the lake.
Since Rice and Koronis are linked by the North Fork of the Crow River, infestation in one body of water would likely expose the other to the exotic species.
The DNR uses mechanical removal as well as chemical treatment of Eurasian watermilfoil. But the extent of their treatment relies on the likelihood of the lake to be the cause of its spread. Where milfoil is established, as in the metro area, the DNR assists local associations and government units in controlling the amount of milfoil in a lake to allow usage of the water.
Where the infestation is small, and the area has few other infestations, as with Green Lake, the DNR will try more aggressively to eliminate the milfoil, to try to stop its spread. Gilbertson said the stands in Green Lake are marked with buoys to try to keep boaters from shredding the plants with their motors and spreading the plant. Also, this fall, they plan on treating the milfoil areas with chemicals to kill the plant. They want to spray when the plant is actively growing for optimum effect, he said.
Cases where Eurasian watermilfoil have been completely eradicated from a body of water are rare.
At Lake Independence, Billo said their best success was in manually removing the milfoil plants using trained divers. Mechanical removal needs to be done very carefully because fragments of milfoil will start to regrow.
Ironically, while a healthy population of weeds indicate a suitable growing environment for milfoil, established weeds can also be a lake's best defense. Where native plants are thriving, it can be hard for milfoil to take root.
A danger of uprooting established vegetation by mechanical means is that milfoil might use this as an opportunity to grow or expand.
Eurasian watermilfoil can be identified by the 12 to 21 leaflet pairs on each leaf. Native Northern watermilfoil has only five to ten pairs of leaflets. (See picture.) Anyone finding Eurasian watermilfoil should contact the DNR immediately.
A false alarm, Billo said, is better than no alarm. "You have to get on it right away," he added, "because it takes over so fast."
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