The Lake Minnetonka Conservation District (LMCD) will create a master plan for handling aquatic invasive species in the lake and probably suspend, at least for this year, its program of mechanically harvesting Eurasian watermilfoil and curly-leaf pondweed.
The conservation district’s decision comes amid criticism from some lake-protection advocates who argue that harvesting the problematic weeds can do more harm than good.
“We passed a resolution late last summer asking for them to halt their harvesting operation,” said Eric Evenson, director of the Lake Minnetonka Association, a nonprofit group of homeowners and business operators. “What we want the LMCD to do is hit the pause button, reevaluate the program and say, ‘Is there a better way of doing this?’ ”
That’s essentially what the district plans to do, said Executive Director Vickie Schleuning. But she disagreed that harvesting is necessarily harmful.
Milfoil was discovered in Lake Minnetonka in 1987 and has spread around the lake, disrupting ecosystems by displacing native plants. It forms a thick mat that can interfere with boating and other recreational water sports.
The LMCD’s harvesting program, which began in 1989, uses boats with underwater blades to chop the problematic weed, collect it in heaps and carry it out of the lake.
This week, the LMCD board voted to hire a specialist to develop a program to control invasive species, as well as analyze its costs and potential funding sources.
Evenson, along with Orono businessman and lake-protection advocate Gabriel Jabbour, said they have spent time researching the problem. They said they concluded that harvesting, in the process of cutting milfoil, also cuts pieces of flowering rush, another invasive plant; if left in the water, the pieces can take root and grow elsewhere in the lake.
“Harvesting is like lawn mowing — you’re taking your neighbor’s dandelions and spreading them somewhere else,” Jabbour said.
Keegan Lund, an aquatic biologist and invasive species specialist for the state Department of Natural Resources, agreed that harvesting can spread invasive species. “A harvester cuts or pulls the vegetation, but the vegetation grows back,” Lund said.
Evenson and Jabbour are among those who favor the use of chemicals. The privately funded Lake Minnetonka Association treats milfoil with herbicide in some bays of the lake and has found it effective.
Not all experts agree, though, that herbicides are the best solution. Chemicals are slower to take effect and generally don’t eliminate all the milfoil they treat, said John Barten, a former director of natural resources management for Three Rivers Park District, which manages parkland along the lake.
“Using chemical treatments in bigger areas and targeted harvesting on smaller areas is about as good as it can get … until something better comes along,” said Barten, who retired in 2015.
Barten, who is chairman of the advisory board for the University of Minnesota’s Aquatic Invasive Species Research Center, said the center is studying other solutions, including introducing a type of weevils that eat milfoil.