Three huge floating cutters normally would be chomping up tons of Eurasian water milfoil this week on Lake Minnetonka. Another would be cutting back weeds in Lake Calhoun in Minneapolis to prepare for the popular Aquatennial milk carton boat races next Sunday.

Not this year.

Permits to harvest the invasive weed have been suspended by the Minnesota Department of Natural Resources because no one from the state is available to oversee the work.

The DNR sent letters and e-mails to dozens of cities, counties, lake associations and private companies just before the July 1 shutdown, suspending all permits that use mechanical harvesters or chemicals to control invasive milfoil, curly-leaf pondweed or other unwanted vegetation.

The Lake Minnetonka Conservation District ran its cutters for four days before the shutdown. Normally they churn through 10-hour days from mid-June to mid-August, clearing water pathways for boaters much like farm equipment harvests crops.

Milfoil is a nuisance on many lakes but especially on Minnetonka. It proliferates in shallow bays and forms dense mats that bedevil boaters.

"Basically they have to go through the mats of milfoil and other vegetation'' that clog boat propellers, said Greg Nybeck, executive director of the district. "They then have to back up and clean it off, sometimes several times."

The district has used mechanical harvesters for 22 years to cut channels through milfoil so boaters can motor through to reach open areas. This year it expected to clear about 400 acres of weedy mats, only a small fraction of the 3,000 acres of milfoil that typically grows on the lake's 14,000-plus acres.

The permit suspensions apply to everyone, including individuals, even if they had a permit and started work before the July 1 shutdown, according to the DNR website.

A letter to permit holders signed by Steve Hirsch, director of DNR's division of ecological and water resources, says all "aquatic plant management" permits are suspended to protect public interest and state natural resources. "Because there will be no DNR staff available to receive notices, inspect aquatic plant control being performed, or inspect mechanical control equipment," he wrote, no weed harvesting or chemical control can be done until state offices have re-opened for business.

That makes no sense to Margy Pennings, owner of Lake Management Inc., a family business at Marine on St. Croix. The company contracts with individuals, counties and lake associations to remove unwanted lake plants by using herbicides approved for Minnesota waters.

Customers are furious, Pennings said, because they can't swim and they can't launch their boats into weed-infested waters.

If the permit suspension continues, she said, people may take matters into their own hands. "It's going to force people to do things illegally, like buying products that are not labeled for use in Minnesota waters, or using them at high doses," she said.

Pennings said her 46-year-old company has never had its business halted, and she disagrees that legal permits already obtained by the company should be suspended.

Pennings said her firm employs five full-time and 12 seasonal workers. She has started layoffs and said she has a "warehouse full of herbicides" that must be paid for.

The DNR listed 37 commercial firms in 2009 that were licensed to harvest or chemically treat aquatic plants. Some have joined forces to ask Ramsey District Chief Judge Kathleen Gearin to cancel the permit suspensions.

Three Rivers Park District has a mechanical harvester, which typically cuts weeds near swimming beaches and boat rental areas in a couple of lakes, said John Barten, natural resources director. "Fortunately a lot of our normal activities have been completed" before the shutdown.

One potential concern is swimmer's itch, caused by tiny water-borne flatworms or blood flukes that can burrow under people's skin. Barten said in some years the district has used copper sulfate near swimming areas to kill snails that release flukes. If cases arise during the shutdown, he said, the district may close beaches or post warning signs because it can't treat the water.

In Minneapolis, the Park Board owns one mechanical harvester and contracts with a private company to cut milfoil and pondweed, said Debra Pilger, director of environmental equipment and volunteer services. The park system clears areas near swimming beaches, boat launches, sailboat moorings and special event locations, Pilger said.

It usually cuts twice each summer in Cedar, Lake of the Isles, Calhoun and Harriet, and once or twice on Wirth Lake. Before the shutdown, she said, the first cutting was mostly done, except on Calhoun.

"If the state gets back in business here soon, we might be able to catch up on this," Pilger said, "but if the shutdown goes on for a few weeks, people will notice a lot more plant growth out there."

Tom Meersman • 612-673-7388