Watermilfoil removal efforts successful at Beaver Lake

Efforts to remove Eurasian watermilfoil from Beaver Lake west of Whitefish indicate the aquatic invasive species may be completely eradicated from the lake within the next few years.

“We will have to be vigilant a couple more years,” said Mike Koopal, executive director of the Whitefish Lake Institute. “It’s unprecedented, once we had Eurasian watermilfoil I wouldn’t have thought we’d be able to get rid of it.”

The invasive species was discovered in Beaver Lake in the fall of 2011. The plants, covering a 12-by-12 foot area in the lake, were found by Department of Natural Resources and Conservation personnel. Since then, efforts to manage the growth and remove the plants have been ongoing.

The Flathead County Weed District originally provided approximately $10,000 in supplies and personnel to address the watermilfoil. Other agencies also became involved in the effort.

Watermilfoil is a threat because it roots itself to the bottom of water bodies and forms dense mats at the water surface shading out native plants, clogging motors and making swimming nearly impossible.

The plant can spread rapidly because it reproduces through stem fragmentation. Pieces the size of postage stamps that have broken off the main stem can reproduce. It’s most often spread overland by boats that have not been cleaned properly.

Efforts in 2012 removed 23 pounds of the plant. In 2013 there was five pounds taken out and in 2014 less than one pound was removed. Less than one pound of the plant was also removed in 2015, according to Whitefish Lake Institute.

Snorkel surveys and diver dredging took place at the end of July 2015, according to Koopal. The entire lakeshore was surveyed and a handful of plants were observed and removed along the shoreline west of the boat ramp.

An increased effort to survey shallow water areas less than one feet deep found some plants east of the boat ramp.

“No regrowth was seen at the area next to the boat ramp or in the two patches west of the boat ramp,” Koopal said. “It is likely that eradication can be achieved within a couple of years.”

Past suction dredging efforts to control the plant have been effective, he added.

This year the institute plans to again use suction dredging, which involves a diver identification survey of single plants or communities and then suction dredging individual plants from the roots to prevent fragmentation. The institute also deploys a sediment curtain near the lake outlet to Beaver Creek to catch any fragments of the plant that may break off during control efforts.

Boaters are reminded to check their watercraft and trailers for suspect material every time they take their boat out of the water. They are also encouraged to wash and dry their boats after each use.

Work at Beaver Lake is part of a multi-approach aquatic invasive species management program the city of Whitefish contracts with Whitefish Lake Institute each year. In institute contracts with Hanson Environmental for the monitoring and control work at Beaver Lake.