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Strands of Eurasian watermilfoil build up in the back of a paddle boat. Volunteer divers were pulling the plant from a portion of the north shore on Aug. 29 during a test of techniques for hand removing it. Submitted photos

Growing urgency drives effort to control Eurasian watermilfoil in beautiful Green Lake

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Growing urgency drives effort to control Eurasian watermilfoil in beautiful Green Lake
Willmar Minnesota 2208 Trott Ave. SW / P.O. Box 839 56201

SPICER -- There's a myth out there that goes like this: Eurasian watermilfoil will never thrive in the clean waters of Green Lake.

Take a look through Greg Swenson's scuba mask, and the reality is much different.


He saw patches of Eurasian watermilfoil in the lake that look like bamboo stands. Individual plants stood six- to eight-feet tall, and in some cases 10-feet tall. They grew as densely as six inches to one foot apart from each other, completely crowding out the native vegetation, said Swenson.

Or, take a look at the Minnesota Department of Natural Resource's data on the problem. Since the invasive species was discovered in the lake in 2000, it has increased in frequency of occurrence from four percent to 20 percent.

Large, monoculture patches of the plant have replaced several historic stands of native vegetation. The plant is growing in sand, rock and rubble substrate where it was not expected to do well. It was recently discovered near the DNR fishing pier at the lake's outlet, where it threatens to spread amongst the native bulrushes.

Swenson is among a small group of volunteers fighting a lonely but urgent battle to keep the invasive species from getting out of control.

"Right now we've got a chance,'' said Ann Latham, a member of the Green Lake Property Owners Association. The association is working under a permit with the Minnesota Department of Natural Resources to control the invasive plant in the lake.

Swenson and four other volunteer scuba divers located new Eurasian watermilfoil infestations on the lake's north shore on Aug. 29. Many of the stands are not visible from the surface, and consequently most people are unaware how widespread the infestation has become.

The divers also carried shovels to attack two separate patches of Eurasian watermilfoil and test what techniques are best for hand removing trouble spots. Swenson said they pushed the shovels in the lake bottom just enough to create puffs of sediment and free the roots. Strands of Eurasian watermilfoil as tall as NBA basketball players were freed and crammed into sacks, which later filled a trailer.

Up above the divers, other volunteers in boats skimmed the water to capture any fragments that might break free. Each tiny fragment is capable of taking root and starting a new colony of plants in the lake.

The plant reproduces both by sending out runners and by what is known as stem fragmentation. Any time a boat propeller slices a plant it can spew out new fragments.

Green Lake's popularity as a recreational lake and its heavy boat traffic means the invasive plant has lots of help in spreading around the lake, said Latham.

The volunteers saw first hand how big of an issue boat traffic is when they dropped white buoys to mark the locations of the newly-identified infestations. The buoys clearly outlined boat traffic patterns in the Lone Tree Bar to Kandiyohi County Park #5 area they worked.

Ironically, there were boaters who motored up to the buoys to see what was going on, churning up the water (and plants) as they did so.

Educating boaters to stay clear of Eurasian watermilfoil is only one part of the solution to controlling the plant, explained Latham.

Its control in Green Lake will also require an on-going, aggressive campaign to knock down stands of the plant with herbicide and hand remove the survivors.

It will also require an equally ambitious program to reduce the sources of nutrients entering the lake and giving Eurasian watermilfoil the opportunity to overwhelm the lake's native plants.

A coalition known as the Green Lake Inlet Partnership is looking for ways to control the inflow of nutrients through the 39 storm water inlets around the lake. Ten inlets have been identified as high priority sites due to the volume of nutrients they carry.

It's no coincidence that the most troublesome stands of Eurasian watermilfoil are located near the inlets, said Latham. The Partnership -- which includes the Middle Fork of the Little Crow Watershed District, Kandiyohi County, the City of Spicer, the Green Lake Property Owners Association and the Minnesota DNR and Department of Transportation asked the Legislature for $780,000 to address the problem. They hope to develop rain gardens and other filters that would keep the nutrients from flowing into the lake.

The funding request made it to third base in the legislative process last year. One of the frustrations, said Latham, is that Green Lake's waters are still relatively clear and not listed as impaired. State funds for water quality projects are directed at impaired waters. Lakes on the "edge," where work now could get head off bigger problems in the future, are often left out, she said.

That hasn't kept the Green Lake Property Owners and others from doing what they can. In the next few weeks $12,000 worth of the herbicide Triclopyr will be applied to the known infestation sites in the lake.

The herbicide is highly effective at knocking down the invasive plant, and allowing natural vegetation to regain its hold in those areas.

Next spring and early summer, volunteer divers will also return to the lake. They are confident that they can be far more effective at hand removing the plants by taking it out early.

There is a lot at stake. Eurasian watermilfoil degrades the water quality of a lake by increasing the phosphorus and nitrogen in the water column. Dense stands of the plants raise the pH level of water, decrease its oxygen content and increase the water temperature.

And of course, the plant crowds out the native vegetation that plays a critical role in the food chain that supports the lake's famous fishery as well.

Eurasian watermilfoil is in the lake to stay, but it can be kept under control no differently than we keep Canadian thistle from over-running our farm fields, according to Latham. But she warns that we need to act fast to keep the infestations from spreading to the point where we will lose the upper hand.

Swenson's dive into the thick stands of the plant showed him just how easily the problem can grow. All of the tall plants had long stems on their upper portions, ready to fragment and spread the plants. "It was kind of scary,'' he said.

Tom Cherveny
Tom Cherveny is a regional and outdoor reporter with the West Central Tribune in Willmar, MN.
(320) 214-4335