Separately, young paddlers have answered the call to river adventures

American literature and film are filled with stories of transformation through high adventure. The best of these feature road trips on blacktop or other conveyances. Think Peter Fonda riding cross-country with Dennis Hopper in "Easy Rider," or Huck Finn adrift on the Mississippi.

Such "heroes' journeys" date to Homer and his tale of Odysseus' 10-year trip after the end of the Trojan War. No one deserves the trouble he encountered en route. But if the protagonists of these sagas don't bump up against calamity and misfortune, and overcome them, heroism can't be achieved.

Joseph Campbell knew this better than anyone. A professor and all-around smart guy who died in 1987, Campbell's 1949 magnum opus, "The Hero with a Thousand Faces," chronicled the "calls to adventure" that often initiate heroes' journeys.

"One may be only casually strolling when some passing phenomenon catches the wandering eye and lures one away from the frequented paths of man," Campbell wrote.

Which describes the happenstance manner in which Sam Mathieu, 23, of Lake Elmo, cooked up his road-trip idea.

"Last August, I was on the St. Croix River near its confluence with the Mississippi, and I don't know why, but I asked the question, 'Do people ever travel the entire length of the river?' " Mathieu said. "Within about 15 minutes of thinking about it, I knew I would try to paddle the length of the Mississippi in a kayak."

Departing the river's headwaters in Itasca State Park on June 3, Mathieu is now somewhere south of St. Louis. Every day, his back, feet and ankles hurt, and in his tent each morning he flexes his fingers for 10 minutes before he can close his hand tightly enough to grip his kayak paddle.

Traveling on a tight budget, Mathieu, a University of Minnesota Duluth graduate (biology and psychology), sleeps at night wherever he can pitch his tent. The trip's first two weeks were the toughest, he said, because the Mississippi near its origin is shallow, buggy and a plague of switchbacks.

"The mosquitoes were so thick up there one night I counted more than 50 bites on my legs just below the knees," he said.

Some days Mathieu paddles 50 miles — in the process, he believes, consuming about 7,000 calories. While waiting for locks to open and move him downriver, he rests. "The other day I had five hours of wait time for locks, and I didn't get off the river until 9:30 at night," he said.

On a similar, but different, waterborne journey this summer is Eric Straw, a 31-year-old Texan. His goal is to paddle his canoe in all 50 states, and last week he checked off waters in Voyageurs National Park and the Boundary Waters Canoe Area Wilderness. (He also paddled in Ontario's Quetico Provincial Park.)

"In 2015 I was listening to an all-sports station in Dallas," he said. "Being discussed was 'The Endless Summer,' the 1960s surfing movie in which two guys surf their way around the world. For some reason that spurred me to thinking I needed to have a six-month-long summer to go canoeing around the country."

"I want to paddle as many free-flowing, natural bodies of water that I can, camping along the way," he said. "For me it's a chance to see parts of this country I've always wanted to see, to be out there alone, and in the ways of Thoreau and Leopold, to shut up and listen to things. To see what happens."

Straw's budgeted expenses include food, fuel for his small SUV, and flights to Alaska and Hawaii, where he'll rent canoes to complete his goal of paddling all 50 states.

Then, like Mathieu, who in addition to his UMD degree is a certified emergency medical technician with plans to become a physician assistant, Straw will head back to the real world.

At least until the next call to adventure is heard.

As Huck Finn put it, "All I wanted was to go somewheres; all I wanted was a change. I warn't particular."