Mounds of matted feathery green noxious weeds were pulled from a small area in Beaver Lake on Monday morning as a group of people dedicated to keeping aquatic invasive species out of Flathead Basin rivers and lakes took aim at Eurasian water milfoil.

Diver Sara Wilkinson of Columbia Falls donned a dry suit to head into the shallow water near the boat ramp to pull up the weed. Wilkinson had fashioned a couple of sticks she thought might aid her in pulling the weeds out, but mostly ended up pulling by hand and by feel, because she was working in “brownout” conditions.

Essentially, any time she tugged at a piece of the 40-foot-by-50-foot patch of the weed, silt was stirred up, eliminating visibility.

Wilkinson repeatedly surfaced handing off bags, about a foot wide and 3 feet long, stuffed with the weeds, to people in two boats. The boat crew, Gordon Jewitt and Don Roe from the Flathead County weed department and Josh Gubits and Lori Curtis from the Whitefish Lake Institute, emptied the bags into giant plastic trash bags inside rubber tubs. The boaters also were armed with nets to scoop up errant chunks of the weed that broke loose.

The plant was especially susceptible to breakage Monday because it becomes brittle in the fall and breaks into fragments that spread across lakes, sinking and starting new plants.

“It’s really fragile,” Wilkinson said as she popped above the lake’s surface. “It’s breaking apart easily.”

After an hour or so of Wilkinson’s work, Jewitt determined it was time to stop pulling and place barriers on top of the weed patch to prevent it from spreading and to prevent sunlight that helps the weed growth from penetrating the water.

The barriers, purchased last week by Flathead County, consist of a heavy, black liner material attached to PVC pipes that are filled with sand to stay on the lake bottom. The barriers will stay in place until next spring when divers will return to the water to remove the weed.

Eurasian water milfoil was confirmed in Beaver Lake, about 6 1/2 miles northwest of Whitefish, on Oct. 19 by Erik Hanson, a biologist and consultant with the Flathead Basin aquatic invasive species work group. The lake was closed to public use on Oct. 24.

Exactly when the lake will reopen hasn’t been determined by Fish, Wildlife and Parks.

Milfoil spreads incredibly easily, Hanson said. That’s why the group immediately developed a work plan. The group plans to meet again this week to continue its discussion for eradication efforts this fall and next spring, Flathead County Weed Superintendent Jed Fisher said.

“This response is what our Flathead Basin work group has been preparing for — to tackle things fast,” Hanson said.

If left untreated, milfoil can become so dense that it prevents recreational use of a lake. It also results in steep declines in fisheries. The resulting effect can be a decrease in lakefront property values by 10 to 15 percent.

“It’s a double whammy to recreationists and property owners,” Hanson said.

How the Eurasian water milfoil found its way to Beaver Lake probably will never be determined, Hanson said. The most likely scenarios are that someone tossed a pet fish from its aquarium into the lake, setting it free, or that a boat carried the weed from some other infested body of water. Milfoil thrives in aquariums, he said.

It’s also impossible to determine how long the weed has been in the lake, but Hanson guessed it’s been growing for about three years.

Hanson said milfoil has been discovered at two other places in Montana: near Noxon on the Clark Fork River and on the Upper Missouri River.

“Those infestations weren’t caught as early as Beaver Lake,” Hanson said. “And they are requiring a much greater effort to eradicate.” Already about $100,000 has been spent on eradication efforts at Noxon, he said.

In the last four years, the state of Idaho has spent $9 million on survey and eradication efforts related to aquatic invasive species, Hanson said.

Monday’s eradication effort was funded in part by a $2,000 grant from the Flathead Conservation District and the Montana Association of Conservation Districts through the Department of Natural Resources and Conservation.

Reporter Shelley Ridenour may be reached at 758-4439 or sridenour@dailyinterlake.com.