Learning to live with milfoil

Note: an update to this story can be found here.

Harvesting of the invasive species is scaled back, and that may not be a bad thing

EAST ISLES — This summer, the milfoil in Lake of the Isles gets a reprieve.

A combination of factors, mainly tight budgets and a rethinking of how best to deal with the invasive aquatic plant, mean milfoil will grow freely in Lake of the Isles even while efforts to harvest it continue elsewhere on the Chain of Lakes.

It’s a decision that won’t please everyone, including those who dislike the sight of thick weed mats floating on the Chain’s crown jewel. But it could be the beginning of a shift toward a more hands-off approach to the aquatic invader (properly called Eurasian watermilfoil to distinguish it from its native cousin, northern watermilfoil).

“It could be a long-term change, depending on what kind of feedback we get [and] what we see out there,” said Tim Brown, environmental operations manager for the Minneapolis Park and Recreation Board.

Some concerns

Not all the feedback Park Commissioner Anita Tabb (District 4) had heard since the decision was announced in late spring was positive. Tabb said some residents of her district complained to her about both the aesthetic and recreational impacts of the decision.

“In general, it was mostly boaters who were having trouble getting through the milfoil,” she said, adding that another invasive clogging Lake of the Isles, curly pondweed, contributed to the problem. “… They’re both invasive plants that are just difficult to get through.”

Tabb, who emphasized the need for both a long- and short-term plan to deal with the invasive species, said she was looking into the possibility of hiring a contractor to do some work over the summer.

“I am trying my very darndest to at least have some kind of harvesting done [this summer] at Lake of the Isles,” she said.

Brown said if he had the funds, he’d do it. But cuts in state aid to cities forced him to slash his milfoil-harvesting budget by one-third, or roughly $50,000, this year.
Lake of the Isles, the most expensive lake to harvest, was dropped from the program.

An experiment

It wasn’t planned to be, but the summer of 2009 was an experiment in the hands-off approach to Lake of the Isles milfoil control.

On the first day of the harvesting season, an overloaded harvester overturned on Cedar Lake. One of only two harvesters owned by the Park Board was put out of commission that day, and still hasn’t been repaired.

It also was a dry summer — so dry that low water levels prevented Park Board crews from floating the remaining harvester through either of two channels into Lake of the Isles, which lacks a boat access. The milfoil went untrimmed, but canoeists and kayakers — the primarily recreational users of the lake — were still able to paddle over the weeds, and water quality improved to nearly the best on record, Brown said.

First discovered in Minneapolis about 20 years ago, invasive milfoil has insinuated itself into the underwater ecosystem. It provides wildlife habitat and also soaks up excess nutrients carried in with storm water, maintaining a delicate balance that limits the growth of algae, Brown said.

The Minnesota Department of Natural Resources, which must approve the Park Board’s aquatic plant harvesting plans, only allows harvesting for recreational purposes, like maintaining boat access and open swimming areas. Besides two canoe launches, Lake of the Isles has neither — although the Park Board in past years cut channels through the thickest weeds for paddlers.

Brown said cutting milfoil might actually contribute to its dominance of the underwater habitat, since tiny, free-floating pieces can sprout new growth. Herbicide, another control measure used in some metro lakes, will also kill native plant species and has been avoided by the Park Board, he added.

No big deal for paddlers

While the Park Board’s remaining paddlewheel-powered harvester unloaded its waterlogged cargo on the shores of Lake Calhoun — where it cleared swimming beaches and sailing lanes in June — small groups of canoeists and kayakers returned watercraft to a nearby rental station. Many had just come through the channel connecting that lake to Lake of the Isles.
Minneapolis residents Roger Peet and Kate Gildner expressed what seemed to be the consensus opinion: The weeds aren’t pleasant, but they aren’t a real problem, either.

“It’s a mess,” Peet said. “The weeds are thick, they’re deep and they’re all the way up to the surface.”

Gildner’s kayak paddle sometimes got tangled in the thick mats of vegetation, but, she said, “It wasn’t that bad.”

Laurie Frame of Eagan and her daughter, Erin Corwine of Seattle, said milfoil didn’t slow them down. When told harvesting on Lake of the Isles was cut to spare plant-control efforts on the rest of the chain, Frame replied: “That’s not a bad trade-off.”