Three months after they dipped their canoe into the Boundary Waters of northern Minnesota, Dave and Amy Freeman stepped ashore on the banks of the Potomac to plead their case in the nation's capital.

For three months, the couple paddled, sailed and portaged the 2,000 miles from the Boundary Waters Canoe Area Wilderness to Washington, D.C. Their canoe is covered, inside and out, with thousands of signatures from people they met along the way, all petitioning the federal government to protect the Boundary Waters from a copper-nickel mining operation proposed near its borders.

"We met people from all across the country who love the Boundary Waters. It's not just people in Minnesota who visit — it's truly a national treasure," said Dave Freeman, who's logged thousands of miles with wife and fellow guide, Amy.

The couple, who were named National Geographic's 2014 Adventurers of the Year wrapped up this year's adventure on the banks of the Potomac on Tuesday, 101 days after they set out. Over the past decade, they have trekked across the country and beyond by kayak, canoe, backpack and dog sled; paddled an 1,100-mile loop around Lake Superior; and once let schoolchildren pick part of their route on a 11,647-mile trek across North America.

But always, waiting for them at the end of their travels, was the peace and tranquillity of the Boundary Waters, a million acres of lakes and wilderness along the U.S.-Canada border. This year marks the 50th anniversary of the Wilderness Act that set aside vast stretches of the northern Minnesota preserve.

The visitors they guide there, Freeman said, "come for the pristine environment, the solitude, being able to sit out in the middle of the lake in your canoe or walk out onto the lake with your snowshoes on — and you can't hear any sounds, there's no lights, there's nothing around you at all. Just the wilderness."

Now, they worry that the peace and pristine beauty of the Boundary Waters could be in jeopardy from the proposed sulfide-ore operation on its borders. Already, Freeman said, he can hear the clatter of test drilling.

Proposed copper-nickel mining operations have divided northern Minnesota communities between those eager for the jobs and economic boost the operations could provide, and those worried about pollution, light and noise spoiling the peace of a region that lures visitors from around the globe.

"These types of mines have a very long track record of pollution. This type of mine in a sulfide-ore body has never been done anywhere in the world without causing significant pollution, both to surface water and groundwater," Freeman said. "The Boundary Waters is a maze of interconnected lakes and rivers. It's really one of the worst places that we could try and put this type of mine."

The Freemans plan to plead their case, and present their canoe/petition, to federal officials they hope can intervene to block the mining operation. The alternative, they fear, will be scenes like the Hudson River Superfund site they paddled through — a place "where you don't even want to touch the water," Freeman said.

"Everyone we met, all along the route, in these non-wild areas, they were all trying to clean up the rivers, they were all trying to gain access to the water," he said. "We have such a special thing in northern Minnesota. You can just go onto the lake and dip your cup in and drink."

Jennifer Brooks • 612-673-4008