“It’s still possible to catch a glimpse of what that wilderness used to be,” says the Canadian filmmaker, painter, author, and conservationist Bill Mason in the opening narration for his cinematic magnum opus, Waterwalker, which turns 40 this year. “And I think the best way to do that is in a canoe, the most beautiful and functional craft ever created.”

Mason was born in Winnipeg, Manitoba, in 1929. His lifelong fixations were evident early on. By the age of two, he was displaying extraordinary artistic gifts, but he flunked first grade for having done little more than draw pictures of canoes while in class.

His family was not wealthy, and so when his parents couldn’t afford to rent a canoe on trips to Lake Winnipeg’s Grand Beach, little Bill would resort to simply sitting stationary in the tied-up rentals. When he was 12, he finally built his own kayak. The kid’s itch to paddle was ungovernable.

To Bill Mason, a canoe was “the most beautiful and functional craft ever created.”

In 1951, Mason received a degree in fine arts from the University of Manitoba, after which he began working as a commercial artist, designing newspaper ads and billboard campaigns. The jobs—often for logging, tire, and trucking companies—went against his deeply held reverence for the natural world, so he would subversively shoehorn messages about the importance of environmental stewardship into his advertising campaigns. Rather surprisingly, his clients loved the work, and he became an in-demand artistic director.

He couldn’t shake nature’s rhythms. Each spring he’d ask his bosses for six months off to make epic canoe odysseys across the wilderness. When they refused, he’d quit. However, when he’d return a half-year later, just as the pristine waters he’d journeyed began to freeze, the bosses would invariably hire him back. He documented his adventures during these explorations of the wild with a Rolleiflex camera, shooting 2¼ in. by 2¼ in. slides. The resulting slideshows became locally famous, with invitations coming in from all over Winnipeg for Mason to exhibit them.

He would subversively shoehorn messages about the importance of environmental stewardship into his advertising campaigns.

One slideshow in particular, “The Timeless Wilderness,” led to documentary director Christopher Chapman hiring him for a film he was contracted to shoot about Quetico Provincial Park, in Ontario. So began Mason’s career as a wilderness filmmaker.

By 1968, Mason’s first film for the National Film Board of Canada (N.F.B.)—“Paddle to the Sea,” based on the 1941 children’s book of the same name—was nominated for an Academy Award for best short film. (The prize went to his mentor, Chapman, for his landmark Expo 67 short, “A Place to Stand.”) His prolific filmography over the next two decades included shorts like “Blake,”a portrait about his “hobo of the skies” pilot friend Blake James, which was also nominated for an Oscar in 1970. His 1972 film, Cry of the Wild, a feature on Arctic wolves, became the N.F.B.’s most successful film ever at the U.S. box office, generating nearly $5 million against a budget just shy of $75,000.

“He couldn’t shake nature’s rhythms.” Bill Mason in Waterwalker.

Mason’s cinematic swan song, Waterwalker, the 1984 masterpiece, predominantly follows his solo canoe journey around Lake Superior. Existing somewhere between a David Attenborough BBC nature documentary and an episode of The Joy of Painting, with Bob Ross, Waterwalker is the summation of Mason’s deepest desire to save the environment by way of showing the transcendent beauty of the unspoiled wilderness. Nature, he says, was “like being in an art gallery. God is the artist.”

The viewer meanders through the most exquisite scenery as Mason quietly canoes, camps, and occasionally runs white-water rapids to a terrific soundtrack courtesy of fellow Canadian Bruce Cockburn. All the while he muses and gently sermonizes in his folksy, idiosyncratic narration. “People look at my tent, and I know what they’re thinking,” Mason says after setting up a large campsite. “They’re thinking, ‘When does the circus begin?’ Let them laugh.”

An awe-inspiring scene from Waterwalker.

The film is also a wonderful showcase of Mason’s awe-inspiring landscape-painting skills; his hero was the 19th-century British master J. M. W. Turner. Instead of using brushes and canvas, he developed a distinctive technique of applying oil paint to paper via a palette knife. The lightweight materials and quick process—paper absorbed the paint much faster than canvas did—were also pragmatic when working out of a canoe.

Bill Mason died of cancer in 1988. In the foreword to his posthumously released collection of essays and paintings, Canoescapes, he described how he wanted to spend his last days: “Painting, writing, smelling the flowers and watching the clouds.”

Waterwalker, along with 15 other Mason films, is available to watch for free on the N.F.B. Web site

Spike Carter is a writer and filmmaker. He is currently working on a book with Scott Thorson about his role as a witness to the Wonderland murders