"The Same River Twice," a documentary chronicling the present-day lives of a one-time group of nudist river guides coming to grips with growing old, is at once startling and unsatisfying. Filmmaker Robb Moss sets forth an ambitious agenda with this sometimes-fascinating film, which incorporates film footage of the 1978 river trip combined with present day video interviews with key participants.

Moss sets the scene via aging documentary film footage of an extended group of friends who were river guides in the Grand Canyon in 1978. He presents them as the epitome of free-spirited hippies who took a month-long trip together. Shot in absolutely ravishing natural light and canyon landscapes, with rushing, clean rivers, the film has an exuberance that shines with young love and optimism.

Flash forward twenty years and Moss focuses on the life paths of five of the aging Baby Boomers. Danny is a married mother living in New Mexico; a former genetics counselor turned aerobics proprietor. Jeff and Cathy are divorced with kids, and Jeff is an author and Seattle radio personality, while Cathy is the mayor of Ashland, Oregon. Barry has three kids, is the director of a psychiatric hospital and mayor (who fails to get re-elected) of Placerville, California. Spaced-out Jim, the most idolized, is an uncompromising simple nature soul, still a single river guide, living in a trailer during winter and contemplating building a "gardener’s cottage," which seems like it will take an eternity to finish.

Director Moss is after a cultural and personal glimpse into fleeting life stages, from youthful, naked idealism to cluttered, compromised adulthood, then forward to a glimpse at mortality and its finality. Only with cancer-stricken Barry do these themes truly resonate, while the others come off as nice, well-adjusted middle-class citizens without fascinating stories to tell.

Many questions linger: Why was that summer critical to their trajectories? Why exactly, was this river trip such a bonding experience? Why was it significantly life-changing, if at all? Why did none of them stay in contact? Most of all, why the heck were they nude so often, and why doesn’t anyone revisiting the footage comment on it?

Moss doesn’t cop to answering any of them, and after awhile one begins to wonder why this particular 1978 summer had any lasting impact whatsoever, though one character does refer to it as "complete experience." There’s no reunion among the friends, and the present day adults seem uninterested in what path the others’ lives took.

What’s best about this film is not the modern day recollections and musings on the finite nature of life’s cycles. There are terrific visual moments here, such as a boat crashing up and down on the waves, camera placed inside at sea level. "The Same River Twice" is most effective when it lets us gaze on its unintentionally poetic, sun-dazed, romantic cinematography of that 1978 trip. If the players themselves don’t elaborate on the significance of the event, the camera itself gives us an up-close glimpse of a perfect innocence and simple grace few of us find in life today or memories.