An environmental group is suing the U.S. Forest Service, arguing the agency is letting outfitters run too many motorized boats to Minnesota's Boundary Waters.

The lawsuit by Montana-based Wilderness Watch alleges the Forest Service has allowed outfitters to top the cap on motorized tow trips allowed each year. The group wants the agency to implement a new permitting process in advance of each season to ensure towboat numbers are held to the legal limit.

Twenty-three outfitters offer towboat services into the Boundary Waters. Many canoeists use the tows for quicker access to Quetico Provincial Park just across the border in Canada. According to the suit, the Forest Service's 1993 plan caps towboat trips at 1,342 per year. The group said data from its freedom of information request show the Forest Service allowed 1,639 trips in 2011 and 2,124 last year.

Towboat traffic is especially heavy on the Moose Lake chain east of Ely, Minn., said Kevin Proescholdt, Minneapolis-based conservation director for Wilderness Watch.

"On typical summer days, the towboats are zipping back and forth, quite a bit on that chain of lakes," said Proescholdt. "And for those of us who prefer to paddle, it really diminishes the wilderness experience when there are these towboats zooming past us again and again and again."

Superior National Forest officials say they can't comment on pending litigation. But motorized access has been at the heart of the controversy surrounding the Boundary Waters ever since the legislation creating the wilderness area took effect on this date in 1979. Subsequent lawsuits have limited the number of lakes accessible to motor boats. Motors are allowed now on part or all of 18 lakes in the Boundary Waters.

Bob Olson, who runs Canoe Country Outfitters in Ely, sees this complaint as another attempt by environmental groups to pull back motorized use.

"To me it's just another way to take all of the motors out, which is their goal," he said. "So they just keep picking away at it. It's just a long line of trying to take things away."

Proescholdt, who was involved in the effort in the 1970s to create the Boundary Waters Canoe Area Wilderness, says that's not the group's goal.

"We're not trying to end motorboat use. We're not trying to end commercial towboat use," he said. "We're trying to get the Forest Service to follow the law."

Outfitters pay the Forest Service 3 percent of their towing fees. At the end of each season, they submit detailed reports. But the lawsuit alleges some outfitters underreported the number of towboat trips made and the number of boats used. Wilderness Watch argues that some outfitters excluded certain tow trips from their reports. The group also says one outfitter reported single "trips" that included 18 boats and 72 clients while others counted separate drop-off and pick-up trips as one single trip.

Mike Prom, who runs Voyageur Canoe Outfitters at the end of the Gunflint Trail on Saganaga Lake, says the claims of a big jump in tow traffic into the BWCA don't match what he's seen and that trips have actually fallen significantly.

"I've been here 23 years, and just from personal experience, there's less tows," he said. "People don't want a tow at 2 in the afternoon, they want a tow right away in the morning, 7 or 8 o'clock, or they'll paddle."