OCEAN BEACH, Calif. — It’s fitting that Nate Dappen turned 35 on Father’s Day. Not only did the San Diego nature filmmaker become a first-time dad in January, he’s also just finished a documentary love letter to his father.

For all of his life, Nate said his dad, Alan Dappen, has been his idol. In Nate’s eyes, the 65-year-old Virginia doctor has been an indomitable adventurer, world traveler and tower of physical strength. And there’s one beloved family story that has always encapsulated his dad’s unquenchable zest for life.

In the summer of 1974, Alan and his brother, Andy, built canoes and with a group of five friends that included Alan’s future wife, Sara Scherr, they spent three months paddling 800 miles up Western Canada’s Inside Passage. They were some of the first people in modern history to make the trip by canoe from Vancouver to Alaska.

“That story became a foundation of my identity, shaping the way I saw my parents and the notion of what it meant to grow up. But you never get the whole story as a kid,” Nate said.

In 2015, he discovered that the well-varnished canoe story didn’t quite live up to the legend. The intrepid ’74 paddlers never actually finished their Passage trek, calling it quits in Ketchikan, 300 miles south of their planned destination, Juneau.

So, last summer the Dappen men decided to made good on their original goal. Nate and his 36-year-old brother, Ben, joined their 65-year-old dad and his 63-year-old brother on a quest to finish the trip and make their legend whole.

That voyage of brothers, fathers and sons in their original canoes is captured in Nate’s new 25-minute film documentary “The Passage,” which he subtitled “A story of growing up, growing old and the wild places that define us.”

Produced by Dappen’s company Day’s Edge Productions, “The Passage” is now available for free streaming on outsidetv.com and Youtube (search “The Passage”).

Alan Dappen said it’s hard for him to watch the film without choking up.

“I was so moved by the fact that he would take a trip that was so meaningful to Sara, myself and my brother and memorialize it in a way that was so beautifully done,” he said. “I don’t need a memorial service anymore. When I die you can just turn on that movie and there you go.”

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A taste for adventure 

Brothers Alan and Andy Dappen grew up in Mexico City and moved so often with their parents they became inseparable best friends. They roomed together in college and when they graduated, the canoe trip seemed a natural fit for the veteran outdoorsmen. But when Sara asked her parents if she could join her boyfriend, Alan, on the trip they asked a psychiatrist to talk her out of it.

The more than 1,000-mile Inside Passage is spectacularly beautiful but it’s also a rainy and icy-cold waterway with 16- to 20-foot tides that create dangerous rapids, riptides and whirlpools.

Fortunately, there were no mishaps on the ‘74 trip, but when summer ended before they reached Juneau, Sara left to return to college. Alan followed her, leaving a frustrated Andy behind. He tried to finish the trip, but without his brother, it wasn’t the same, so he gave up.

Now a resident of Washington state, Andy would go on to become an adventure journalist and photographer writing for numerous sports magazines and newspapers. Alan married Sara in 1978, and during his medical residency in California in the early 1980s, Ben and Nate were born.

The young family next moved to Kenya for five years. Sara, an agriculture economist, studied crop breeding in Nairobi while Alan and the boys spent their days studying nature and wildlife, rock-climbing and hiking in the bush.

In the years to come, the Dappen men would go on African safaris, scale the Cascades Range and canoe the Pacific Northwest. By age 10, Nate and Ben were doing solo homestays in Latin America to learn Spanish. At 17, Nate hitchhiked alone across Australia. And after college, he followed a girlfriend to Italy and stayed for three years.

He credits his parents with instilling his confident spirit of adventure.

“Both of my parents have been undaunted by the challenges of life and overcoming obstacles,” Nate said. “From them I’ve learned the idea of going out actively and creating experiences rather than letting life happen to you.”

But Nate wasn’t an easy child. In his early teens he got into trouble with drugs and the law and crashed his father’s car.

“He was one of those kids who pushed every rule you made and was a good wheeler-dealer,” Alan said.

Like his father before him, Nate become a high school wrestler. One opponent he could never beat was his dad, who never cut his son any slack when they’d face off on the mat. Finally, when Nate was a senior, he came close to beating his dad, but Alan says he tapped out and “retired” on the spot to keep his record unbroken.

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Capturing the wild 

Nate’s initial career goal was to be a doctor, like his dad, but he ended up focusing instead on evolutionary biology. In 2008, he was doing jungle field work in Costa Rica for his Ph.D. when he met fellow Ph.D. candidate Neil Losin and they discovered a shared passion for nature photography and film.

Within two years they would both abandon their academic pursuits to found Day’s Edge, which has produced numerous educational, broadcast and advocacy films about nature, wildlife, agriculture and the environment. Clients include National Geographic, PBS, World Wide Fund for Nature and the Smithsonian Channel.

Most of their projects make money, but Nate and Losin, who lives in Florida, allow each other the occasional self-funded passion project, like “The Passage.”

The idea for the canoe trip and movie were hatched in September 2015, when the extended Dappen family was gathered for Nate’s wedding to Amanda Dappen, a family doctor now in residency at Scripps Memorial Hospital in Chula Vista.

Nate and Ben were eager to join the canoe trip because they’d heard about the Inside Passage trip their whole life and hoped to be of help to their aging dad and uncle.

“Ben and I had noticed how our dad defined his life by what he could achieve physically. That was his identity. So when you can physically outperform your parent, the reality sets in that they’re getting older,” Nate said.

Some of those fears were realized when Alan suffered a fall during the trip and Nate’s tearful worries are captured on film.

In two canoes, the Dappen men spent two weeks last summer paddling and filming from Ketchikan to Wrangle. There, Ben left to return home to his family in Portland, Ore., where he runs an electronic medical records firm, and Nate returned to Ocean Beach, where his wife was expecting their first child. Alan and Andy were more than happy to paddle the final leg of the journey to Juneau alone.

The film — which debuted online this week in honor of Father’s Day — ends with the news that Nate and Amanda’s daughter, Juniper Marie, entered the world on Jan. 25. He said this week that the experience of fatherhood has stirred up memories about his own extraordinary childhood.

“Parenting my own child, I feel a tremendous amount of pressure,” he said. “Ben and I have a tremendous amount of hero worship for our parents. I don’t know how I’ll ever live up to it as a dad myself. I can’t replace those experiences but I can make the outdoors a big part of our lives and, like my parents, I can support all her dreams.”